Lighting for Interior Design PDF

www.ebook3000.com Lighting for Interior Design Published in 2012 by Laurence King Publishing Ltd 361–373 City Road London EC1V 1LR Tel +44 20 7841 6900 Fax +44 20 7841 6910 E [email protected] www.laurenceking.com © Text 2012 Malcolm Innes This book was produced by Laurence King Publishi...

www.ebook3000.com Lighting for Interior Design Published in 2012 by Laurence King Publishing Ltd 361–373 City Road London EC1V 1LR Tel +44 20 7841 6900 Fax +44 20 7841 6910 E [email protected] www.laurenceking.com © Text 2012 Malcolm Innes This book was produced by Laurence King Publishing Ltd, London Malcolm Innes has asserted his right under the Copyright, Designs, and Patent Act 1988, to be identified as the Author of this work. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any information storage and retrieval system, without prior permission in writing from the publisher. A catalogue record for this book is available from the British Library. ISBN 978 1 85669 836 8 Designed by John Round Design Printed in China Title page: One Gyle Square, Edinburgh, lighting design by FOTO-MA Opposite: Section drawing of lighting scheme for the Musée de l’Orangerie, Paris, by Anne Bureau Concepteur Lumière www.ebook3000.com Lighting for Interior Design Malcolm Innes Laurence King Publishing Contents 6 INTRODUCTION 36 3. Natural light 36 What do humans need? 7 About this book 38 Sources of natural light 40 Range of intensity 41 Direction of natural light 8 PART I THEORY 42 Color and natural light 45 Daylight control 10 1. The physics of light 46 Case study: Architecture Gallery, 11 What is light? Victoria & Albert Museum, London, UK 12 The physical properties of light —what designers need to know 48 4. Electric light 13 Reflection 49 Sources of electric light 14 Mirrors 49 Incandescent light sources 15 Transparency 50 Discharge light sources 16 Filters and lenses 55 Electroluminescent light sources 18 Refraction 57 Luminaires 19 Shadows 58 Nondirectional and directional luminaires 20 What is color? 59 Concealed luminaires 24 Quantifying light 59 Manufacturer’s data 25 Luminance 60 Generic luminaire types 25 Candela 62 Visualizing patterns of light 25 Lumen 64 Visualizing spotlight data 25 Luminous flux 65 Isolux diagrams 25 Foot-candle 66 Lighting control systems 25 Lux 68 Line voltage dimming 25 Illuminance 70 Electronic dimming 25 Light meters 26 2. Human factors 26 Sensing light 27 Adaption 28 Experiencing changes in light levels 29 Eyes and the sense of sight 30 Stereo vision 32 Motion detection 33 Low light sensitivity 34 Light and psychology 34 How do we see? 35 Preferences Related study material is available on the Laurence King website at www.laurenceking.com www.ebook3000.com 72 PART II PROCESS AND PRACTICE 140 9. Recording and visualizing lighting 141 Drawing and sketching 74 5. Lighting principles 142 Abstract representation 74 Visual hierarchy 144 Diagrammatic representation 76 Understanding qualities of natural light 146 Photography 77 Understanding layers of light 148 Computer renderings as a design tool 79 Change and variation 150 Physical models 80 Creating drama through lighting 82 Changing and controlling light 154 10. Project communication 86 Surfaces and texture and completion 155 What is enough information? 88 6. Lighting for people 156 Sections and elevation drawings 88 How much light is enough? 158 Case study: Musée de l’Orangerie, Paris, France 90 Lighting for comfort and safety 162 Light renderings 91 Task lighting 164 Step by step: Using computer models 92 Lighting for orientation 166 Recording circuiting and control intent 94 Step by step: Lighting a corridor 168 Use of sketch details 96 Case study: Wayfinding: Terminal 2F, 170 Lighting mock-ups and tests Charles de Gaulle Airport, Paris, France 172 Specification documents 98 Avoiding glare 172 Generic specification 100 Case study: Low light gallery, St Mungo’s Museum 172 Detailed specification of Religious Life and Art, Glasgow, UK 174 Realizing the project 175 Final focusing and programming 102 7. Lighting for architecture 102 Ambient lighting 106 Accent lighting 178 Conclusion: the future 110 Case study: One Gyle Square, Edinburgh, UK 184 Glossary 114 Case study: Sheikh Zayed bin Sultan Al-Nahyan Mosque (The Grand Mosque), Abu Dhabi, UAE 186 Further reading 120 Lighting vertical surfaces 187 Index 121 Integrating light with architecture 191 Picture credits 122 Case study: Morimoto Restaurant, Philadelphia, USA 192 Acknowledgments 126 8. The design process 128 Researching the project 128 Analysis of needs 129 Outline proposal stage 129 Construction document stage 129 Construction stage 129 Final focus and programming 129 Client handover 130 Case study: St Machar’s Cathedral, Aberdeen, UK 6 Introduction "A common man marvels at uncommon things; a wise Light reveals color and three-dimensional form, while man marvels at the commonplace." directional plays of light expose the texture of surfaces and Confucius materials. These elements are so integral to the appreciation of space that without the carefully considered and appropriate Light surrounds us every day; it is the epitome of application of light, interior design can never be truly great. “commonplace,” and this familiarity can prevent us seeing Light has the power to influence the mood and its wonder. It affects our sleep patterns and working hours, atmosphere of space. Altering the patterns of light, shade, our alertness and health. Yet the power and importance and color can make the users feel relaxed or alert; warm and of light are often overlooked by those who shape our built comfortable; cold and uneasy. Light and color can be used environment. Hopefully, this book will encourage readers to make users feel stimulated or subdued. Skillful use of light to marvel at the commonplace and so help them produce allows us to imbue interior designs with the sensations and great architecture. emotions we want users to experience. The word “vision” has grown beyond its Latin roots Given the importance of light and color within interior (from the word videre meaning “to see”). “Vision” now design, it is surprising how often lighting seems accidental includes all that can be imagined and dreamt. But it still and extraneous. Light is intangible and immaterial, which also defines the act of seeing—and it is light that makes seems to imply that it is also uncontrollable, but interior the world visible, and light that allows us to make sense design is fundamentally about the manipulation of space— of our surroundings. Despite this, the importance of light another immaterial property. in architecture is often underestimated. Great architecture As with architecture and interior design, lighting design and interior design thrill the senses, but consider how little is neither an art nor a science, but a synthesis of both. It is of our built environment is experienced in any way other a subject that is often clouded by technical terms, complex than through our sense of sight. Without light, interior physics, and mathematics. But at its core lies a simple truth: architecture simply cannot be fully experienced; it is invisible we were all born with an innate appreciation of light and to us. However, light can influence much more than just our color, and all our favorite built environments draw deeply visual experience of architecture. from that well of experience. Left Musée de l’Orangerie, Paris. Lighting by Anne Bureau Concepteur Lumière. Careful lighting design was integral to the success of this gallery conversion. www.ebook3000.com  About this book 7 About this book This book is an introduction to the subject of architectural lighting design. It intends to explore the aesthetic and emotional capabilities of well-designed lighting without obscuring the subject behind science and mathematical formulas. Dramatic and visually stunning projects are illustrated throughout, but this is not just a picture book. The work of some of the world's leading lighting design practices is analyzed in detail to explore some fundamental principles of this field. The book is divided into two parts. The first part, Theory, explains the physical properties of light and its physical and psychological effects on humans. It outlines elements of natural and artificial light, including a discussion of types of luminaire and control systems. The second part, Process and Practice, first covers practical lighting principles, good design for human needs, and how to light surfaces and spaces. It then focuses on the practicalities of presentation for clients and others: how to record lighting systems, and communication from initial sketches and test models through to providing specifications for contractors and the all- important on-site finalization. All these elements are crucial in realizing a successful lighting design project. Above right Copenhagen Opera House interior, lighting by Speirs and Major Associates. Good lighting design not only enhances occupants’ experience of an interior space, but can also, as in this case, help visitors move through a space. Right Copenhagen Opera House. A good designer will also consider how lighting affects a building’s exterior. www.ebook3000.com PART I THEORY 10 1. THE PHYSICS OF LIGHT 26 2. HUMAN FACTORS 36 3. NATURAL LIGHT 48 4. ELECTRIC LIGHT 10 Theory 1. The physics of light Light elicits both physical and emotional reactions from As Albert Einstein observed, “The work of James human beings. We have a “human” response to light. But Clerk Maxwell changed the world forever.” Einstein had in objective and scientific terms, what is light? Even in the no doubts about the importance of Clerk Maxwell’s work objective world of the scientist, light is often confusing to his own; he described the physicist’s work as, “the and contradictory. The nature of light has been a subject most profound and the most fruitful that physics has of philosophical and scientific inquiry for centuries. experienced since the time of Newton.”1 For a medium Man has been trying to identify it since the time before that governs so much of our lives, two remarkably simple mathematics and physics. questions can demonstrate how little most of us know Despite thousands of years of human inquiry, about the nature of light: “What is light?” and “What remarkably little was understood about light beyond its is color?” basic observable features before the eighteenth century. 1 “James Clerk Maxwell” in Encyclopædia Britannica, 2010, Encyclopædia It was observed that light travels in a straight line; that Britannica Online, 4 May, 2010, polished surfaces such as mirrors reflect light; and that http://www.britannica.com/EBchecked/topic/370621/James-Clerk-Maxwell crossing beams of light do not interfere with each other. It was not until Sir Isaac Newton published Opticks: A Treatise on the Reflections, Refractions, Inflections and Colours of Light in 1704 that the true nature of white light was widely understood. However, the greatest leap in the understanding of light was achieved in the nineteenth century by the physicist James Clerk Maxwell. His 1864 work entitled A Dynamic Theory of the Electro-Magnetic Field established the fundamental truth of light: that light is energy. Right Industrial lasers can concentrate vast amounts of light into a very small area, creating enough energy to cut through sheet steel. www.ebook3000.com  The physics of light 11 What is light? Light, as we have said, is energy. It is part of the Below electromagnetic spectrum that includes radio waves, Visible light is just a small part of the spectrum of electromagnetic microwaves, X-rays, infrared, and ultraviolet. These are radiation, which includes X-rays, all forms of electromagnetic radiation, the difference microwaves, and radio waves. being in the wavelength (and therefore energy level) Radiation with wavelengths of the radiation. Visible light is simply that: visible between about 380 and 750 nm is the only part of the spectrum energy. It is electromagnetic energy in a range that that we perceive as light. Infrared our visual system is sensitive to and that gives us energy is experienced as heat. the sensation of sight. In contrast, although infrared radiation is also electromagnetic radiation, our eyes are not sensitive to it. We get no sensation of sight from infrared; instead, we perceive it as heat. As light is a form of energy it obeys physical laws that apply to energy, including the laws of thermodynamics. The first law of thermodynamics states that energy cannot be created or destroyed; it can only be transformed from one kind of energy into another. Light can be produced with heat, where an object becomes so hot that it radiates energy as Gamma rays Gamma rays light. Light can be produced by the transformation of chemical energy. Visible light can also be produced by - 0.1 nm the transformation of other kinds of electromagnetic energy, such as ultraviolet or microwave energy. X-rays X-rays - 1 nm There is evidence all around us of the energy increasing energy level embodied in light. Solar cells transform the energy in visible light to electrical energy; industrial laser increasing energy level - 10 nm cutters are used to cut intricate patterns in everything Ultraviolet Ultra Violet from delicate paper to the toughest steel plates. But - 100 nm the most ubiquitous transformation of light energy is found among plants. Plants use the power of visible Visible light Visible Light - 1,000 nm light to convert carbon dioxide and water into food (a process called photosynthesis). The human visual Infrared - 10 um system converts light energy entering the eyes into Infra Red chemical energy that is used to communicate the - 100 um information received by the eye to the brain. - 1⁄32 in Microwaves - 3⁄8 in Microwaves increasing wavelength - 4 in Television Television - 3 ft increasing wavelength FM radio FM Radio VHF radio VHF Radio - 30 ft - 300 ft AM radio AM Radio - 3,000 ft Long-wave radio Long Wave Radio Wavelength 12 Theory The physical properties of light —what designers need to know Although this book is about designing with light, and is not a physics textbook, we need to understand some basic properties of light before we can use it effectively in the built environment. The more we understand about the physical properties of light, the easier it becomes to use it creatively. The most basic property of light is that it travels in straight lines if it does not encounter other materials. Also, a beam of light is invisible to us unless it strikes materials such as a solid surface or dust; it becomes visible when it hits something that reflects some light toward our eyes. Materials that we would describe as white or light-colored appear so because they reflect more light than dark ones. (However, it is not simply the quantity of light we put into a space that makes it seem bright. It is the reflective properties of the surfaces in that space. A black-painted room will always appear dark, no matter how much light we put into it.) Polished surfaces produce specular reflections. Specular means “like a mirror,” and a good specular reflection will not distort the beam of light. This enables us to have mirrors that give us an image of ourselves as others see us. Specular reflectors maintain the integrity of a beam of light, and light striking the reflector at an angle will be reflected at an equal and opposite angle. If we shine a torch at a mirror, we have to look at the mirror from the correct angle to see the reflection of the torch beam. Very matte surfaces produce diffuse reflections. A perfectly diffuse reflector will reflect light equally from all angles. A sheet of plain white printing paper is close to being a perfectly diffuse reflector. The light beam is disrupted when it hits the surface of a diffuse reflector and light hitting the surface at an angle loses any direction in the reflection. Whatever direction we see the sheet from, it TIP opaque materials appears to be equally bright. Despite frequent misuse, the term A common misconception is that shiny surfaces “opaque” only has one meaning; opaque reflect more light than matte ones. This is not necessarily materials are not transparent and true; the difference lies in the direction in which the cannot be seen through—they pass no surface reflects the light. The mirror could appear dark light. When most people say “opaque” when viewed from a position where the light source they actually mean “translucent”. A cannot be seen, while if the white paper is lit by a torch it translucent material, such as etched appears equally bright wherever we view it from. glass or tracing paper, does not permit clear vision, but does allow some Light travels in a straight line, but when it moves light through—it is semitransparent. from one transparent medium to another its path can be Therefore, it is essential when speaking bent. This process is called refraction and happens when about light to use this terminology light passes between materials of different optical density correctly and to question others closely (measured as the refractive index). A shaped glass lens will to determine what they actually mean. bend light traveling from the air through the glass to bring After all, a truly opaque window is rather it to a focus at some point beyond the lens. pointless, but frosted or etched glass has many uses. www.ebook3000.com  REFLECTION It is the interaction between light and surfaces that defines our change of wall covering or the addition of a mirror or glazed visual impression of materials, objects, and spaces. Without painting can dramatically alter the lit appearance of a space. light, surfaces remain unseen, and without a surface to interrupt An understanding and consideration of reflection is therefore an a beam of light, the light itself remains unseen. A simple essential component of any lighting design. 1 A standard glass mirror is a good approximation for a perfect reflector. Following the laws of reflection, a beam of light hitting the mirror at 2 White paper only produces a soft reflection. Although the light hits the surface at an angle, the reflection has no direction. The light is 3 Polished aluminum can produce specular reflections like a mirror. If the polish is not perfect or the surface is not absolutely flat, the an angle will be reflected back at the equal and reflected pretty equally in all directions. This is a reflected image will be imperfect. opposite angle. This is a specular reflection. diffuse reflection. 4 A nonpolished reflective surface, such as (unpolished) mill finish aluminum, is halfway between a perfect reflector and a diffuser. The 5 A glazed ceramic tile produces a diffused reflection from its white pigment and a specular reflection from the glaze. In this image, the light 6 Whether it is polished or matte, a colored surface will impart some of its color to the reflected light. The beam of light that hits the resulting soft, diffuse reflection can still have a hitting the ceramic tile has produced a soft orange wall is white, but the reflected light on real direction to the beam. This is described as glow over the ground plane as well as a distinct the floor is tinted with the color of the wall. a semispecular reflector. reflected line on the right of the picture. The bright angled line on the left of the tile is a reflection of the incoming beam of light on the ground.  MIRRORS Although lenses are used in many types of lighting equipment, the positioning of a light source. Instead, combinations of curved the majority of luminaires use reflectors to control the direction mirrors and textured surfaces are used to produce a more even and spread of light from a source. Most reflectors are made from spread of light. Nonperfect reflectors are favored because they polished aluminum or mirror-coated plastic. Flat, perfectly mirrored allow greater tolerance in the positioning of a light source and so surfaces are rarely used because they require great accuracy in produce less variation between different luminaires. 1 This curved Mylar sheet has a mirrorlike finish. The curve means the incoming, parallel beams of light hit the reflective surface at different angles and this produces the pattern of reflection. Here the parallel beams of light 2 Lighting reflectors are often made from materials that are not perfectly flat mirrors. This aluminum sample has a mirrored finish, but it is also highly textured. This produces a specular reflection but the patterning introduces are entering from the lower left of the picture and are being reflected to meet some variation to this, which widens the spread of light and also introduces at a point in front of the curved reflector—the focus of the curve. It is easy to some sparkle where light is reflected toward the viewer. Textured materials see that, with a light source placed at the focus point, a parallel beam of light such as this are often used in luminaire reflectors to “soften” light from very would be produced by this reflector shape. intense sources. www.ebook3000.com  TRANSPARENCY Light can pass through various materials, and these are window glass interferes with light, only transmitting a proportion described as being transparent. With most such materials we of the light striking it and completely blocking parts of the tend to think that all light passes through, and indeed a physical nonvisible spectrum. Nevertheless, transparent materials are an definition of transparency is that heat or electromagnetic essential feature of our built environment; to design with light radiation can pass through without distortion. However, even you must understand how it interacts with these materials. 1 A transparent material can never pass 100% of the light that hits it. The polished surface of this piece of thin acrylic sheet reflects some of this 2 The more acute the angle of the incoming light, the more light will be reflected. In this example a sheet of glass is set at a very acute angle 3 At some point the incident angle of the light becomes so shallow that no light can pass straight through the transparent material and light. Normal window glass typically transmits a to the beam of white light. Most of this light is all the light is reflected. Where the light is maximum of around 80% of the visible light that reflected by the glass, resulting in a significantly directed at a very shallow angle into the edge reaches it. darker line of transmitted light. of a transparent material such as this sheet of glass, the light is reflected by the inside surfaces and bounces along the length of the sheet to emerge at the other end. In this case, the light is distorted by imperfections in the surface of the glass. It has also taken on a green tint after traveling through the equivalent of a 6 in-thick piece of glass. 5 Fiber-optic cables are designed to redirect light by the process of total internal reflection. Rather than using one large rod, fiber-optic cables are usually made from a number of smaller strands. This gives them great flexibility and allows them to be bent into tight curves without losing light. This small bunch of plastic fiber optics captures some of the light from the green, blue, and red beams of light and transports it along the whole length of the strand to emerge at the other end. Fiber optics for lighting are very good at 4 This acrylic rod interrupts the green beam of light and, through internal reflection, the light is transported along the rod to emerge at the transmitting visible light, but poor at transmitting infrared (heat). This feature allows a hot light source to be separated from heat-sensitive other end. materials that are to be illuminated.  FILTERS AND LENSES Many materials transmit more light than they reflect. We tend to more it will tint the light. Other materials impart strong colors, call most such materials “transparent,” but transparent materials diffuse light, or otherwise alter beams of light in some way. still filter transmitted light to some degree. Window glass tints Designers can harness these material properties to control the light with a very subtle green tinge. The thicker the glass, the color and spread of light within their designs. 1 Clear transparent materials allow light to pass through without significantly altering the color or spread of the light. 2 The term “opaque” is often misused, but it has only one meaning. Opaque materials prevent any light passing through. This image shows an 3 Translucent materials like frosted glass, tracing paper, or the theatrical filter used in this image allow light to pass through but diffuse the beam. Different opaque card interrupting the beams of light and materials diffuse the beam to different extents; this casting a shadow onto the wall beyond. theatrical diffusion filter produces beams that are very indistinct at any significant distance beyond the filter. 4 This theatrical filter is a light frost and, like a lightly etched piece of glass, it softens the beams of light a little but the beams remain 5 Colored transparent materials allow light of certain colors to pass through, while blocking other colors. This theatrical filter allows red light 6 This green-colored filter absorbs all the colors apart from green. The red light here contains very little green light and therefore appears very distinct. This level of diffusion is not suitable for to pass through. The green, red, and white dim compared to the other colors. creating a light box or backlit panel, because beams all have some red light in them, so the lamps would be clearly visible. this passes through while the other colors are absorbed by the filter. The blue light contains no red, so no light passes through the filter. www.ebook3000.com 7 While the green, blue, and white light beams all contain some blue light, the red beam has no blue light and is greatly darkened by the 8 This sample of frosted glass does not completely diffuse the light, but it produces a very soft-edged beam of light on the wall 9 This transparent convex lens bends the light to an equal extent in all directions, creating a circular beam of light. blue-colored filter. A very small amount of light behind. This kind of diffusion filter is designed to is visible in the red beam, but this is largely soften the beam of a narrow spotlight. because the filter material is not a perfect blue and is not a good block to the infrared part of the spectrum. This allows a little bit of visible red light through, which mixes with the general wash of blue to make a dim purple band where the red line should be. 11 This glass filter is transparent but is cut into a fluted shape on one side. Acting like a set of cylindrical lenses, this filter spreads the light in one plane creating an elliptical beam of light. This kind of lens is often used to spread the light of a circular spotlight to effectively illuminate tall objects in museum displays; hence it is commonly known as a sculpture lens or simply as a spread lens. 10 This cylindrical acrylic rod acts like a two- dimensional lens. Light is refracted by the lens, but only in one plane. The white beam of light has been spread horizontally but not vertically by the lens. White screen Filter or lens Right Diagram illustrating how the investigations Digital projector illustrated on these pages were achieved using a digital projector.  REFRACTION Light travels in a straight line, but when it passes obliquely of the transparent material. This process of refraction allows through transparent materials of different densities it can be our eyes to bend the light passing through our pupils so that it deflected. The extent of the deflection is determined by the is focused on the retina at the rear of the eye. Refraction also density of the elements through which the light passes (such as allows us to create lenses that bend and deflect beams of light glass and air) and the angle at which the light meets the surface in such devices as DVD players, telescopes, and projectors. 1 This glass of water refracts the focused beam of light, spreading it out into a blurred pattern on the surfaces beyond. The amount of refraction is affected by the angle at which the light hits the surface of the object. The varying 2 At this angle the acrylic prism produces both reflected and refracted images. Some of the light reflects off the polished surface and hits the rear wall on the left. Some of the light enters the prism and is refracted so that it comes curves on the glass bend the light to different extents. out at a different angle and hits the rear wall on the right. Lenses work by refraction—bending the light to give the light beam a new direction. 3 The refraction process actually bends the different wavelengths of light by different extents. In this image, the line of white light is separated by the prism to show its component colors. www.ebook3000.com  SHADOWS It is often overlooked, but designing a lighting scheme also of light sources, their locations, the direction in which they focus means designing the location and depth of shadows. Lighting their light, their relative intensities, and their distance from an design is not about eliminating shadows, rather making best object. Shadows are a vital clue that our visual system uses to use of them. A great deal of information about the light in a interpret the three-dimensional shape and texture of objects in space can be inferred by the nature of a shadow: the number our field of view. 1 A diffuse light source close to these perforated patterns barely casts a shadow. The star pattern is about halfway between the light source and 2 Move the light source a little farther away and shadows begin to appear. The sharpness of a shadow is proportional to distance, so the 3 Move the light source even farther back and the shadows become more distinct. the wall beyond. relative distances between light source, pattern, and the surface beyond affect the quality of the shadow. Notice that the pattern closest to the rear wall casts the clearest shadow—the distance from light source to pattern is much greater than from pattern to wall. series of positions for the rectangular diffuse light source used for shadow demonstration. 4 Even with a very diffused light source, a sharp shadow can be created if the distance between the source and the object is many times greater than the distance from the object to the surface beyond. In this case, the distance ratio for the star pattern is about 10:1. 20 Theory What is color? Color is an incredibly important feature of our visual story: there are conditions when the orange and the car world, yet it is very difficult to describe what it is. Not only do not appear to be the colors we expect. When we say a is color difficult to define, it does not exist in the way we car is red, what we actually mean is that under white light tend to think of it. At the most basic level, we respond to conditions the paint pigment on the car reflects mostly different wavelengths of light with the sensation of color. red light. This is an important variance on how we usually Isaac Newton’s famous experiments with sunlight and describe color and objects. prisms—replicated in every rainbow—proved that white light is a mixture of colors. We often think of color as an intrinsic feature of an object or material—the rind of an orange is orange-colored and a red car is red-colored. But this is not the whole Right Gamma rays rays Gamma When white light is passed through a glass prism, the different - nm - 0.1 - 0.1 nm wavelengths of visible light are 400 400 nm nm separated so that we can see Violet Violet the individual colors that were X-rays X-rays - 1 -nm- 1 nm combined to make the white light. - 10- nm - 10 nm Blue Blue Ultra Violet Ultraviolet 500 500 nm nm - -nm - 100 100 nm Green Green VisibleVisible Lightlight - - 1,000 - 1000 nm nm Yellow Yellow InfraInfrared - 10 um Red - 10- µm 600 600 nm nm - 100 um Orange Orange - 100 - µm - 1⁄32 in - 1 -mm - 3⁄8 in Red Red 700 700 nm nm Microwaves Microwaves - 1 -cm Above Right A rainbow produces the same The whole of the electromagnetic - 4 in - 10- cm effect as a prism. Raindrops in the spectrum is made up of different Television Visible Light Visible light sky bend the different wavelengths wavelengths of radiation that have Television - 3 ft of sunlight to different extents, different properties. The small FM radio- 1 -m which leads to the characteristic section of radiation we perceive FM Radio VHF radio arcs of color in the sky. as visible light covers a range of VHF Radio - 30 ft wavelengths from around 380 - 10- m to 750 nm. Within that band, different wavelengths give the - 300 ft sensation of different colors, with - 100 - m AM radio red centered around 700 nm, AM Radio green around 530 nm, and blue - 3,000 ft - 1 km around 470 nm. Long-wave - Long radio Wave Radio wavelength Wavelength www.ebook3000.com  The physics of light 21 A B C D Above This children’s toy is made of C All the colors are still discernible brightly colored components. The under a pale green light, but they various parts would normally be seem to have become anemic described as being red, white, and have lost all their vibrancy. blue, green, or yellow. D Under strong blue light the A However, this description is components lose almost all sense based on what the toy looks like of their white-light colors. The under white light. green roof and yellow bucket B When lit with only red light, the appear to be the same color, and colors of the components seem to the blue body and white window shift, with the blue and green parts look as though they could be the becoming much darker and the same material. The red tires are yellow taking on an orange hue. totally unrecognizable. 22 Theory Top The apples only display their green and red colors under white light. Center Using colored light turns the green apple orange. Bottom Seen under a deep blue light, the red apple becomes very dark and looks more like a plum than an apple. www.ebook3000.com  The physics of light 23 Left The top image shows a colored juggling ball illuminated with a single white light source, while in the bottom image the light source is filtered to be blue on the left and red on the right. As white light contains all the colors of visible light, the juggling ball can be seen as an object made from panels of different-colored materials (top). The pigment in the top panel reflects red light most strongly and the front panel reflects blue light most strongly; under white light, we see these panels as red- and blue-colored materials. However, when the same ball is seen under pale blue and pale red light (center), there is a remarkable transformation. When the top panel is illuminated by a blue light, which contains no red component, the material becomes dark. Under the red light, the top panel reflects red and so retains its color. Under the red light, the front panel has no blue light to reflect and so it also becomes dark. In this example, the colors of the two lights are such that the top panel in blue light becomes a very close match for the front panel in red light—simply changing the lighting has completely altered our perception of these materials. We tend to believe that the colors we see in this toy are an inherent feature of the materials the toy is made from; in fact, the colors we see are a feature of the light that illuminates the object. red and blue ball seen in colored light White screen red and blue ball seen in white light Digital projector 24 Theory Quantifying light We have a remarkable visual system that performs consistently over a wide range of lighting conditions, but there is one thing it cannot do: it cannot enable us to measure quantities of light just by looking. We often talk about “brightness” as if it is some form of measurement, but the best that can be said is that brightness is a perception, not an absolute. A single candle flame in a dark room appears to be very bright, but can hardly be seen in daylight. The sensation of brightness is also subjective. A person who has spent a lunch hour in a dimly lit restaurant may perceive some areas of the space as being quite bright. Meanwhile, another person walking in from the sunny street outside will see the whole restaurant as being dark. What we think of as our built-in brightness scale is a contrast measurement, a relative assessment based on the surrounding light conditions and the conditions we have recently experienced. What is most remarkable about this is that our built-in assessment is constantly adjusting to suit our surroundings. This allows us to move between very light and very dark spaces, but prevents us having any real sense of measurable quantities of light. Luckily, there are standardized measurements of light that do not rely on personal judgment. Unfortunately, they are standard physical units and the definitions can be quite complex. The descriptions presented here are simplified and are as technical as is necessary in this book. All lighting units are interlinked, so despite the simplifications some definitions can be difficult to decipher without reading other terms. Hopefully, a couple of readings will make things clear, and further information can easily be found in printed and online dictionaries. www.ebook3000.com  The physics of light 25 Luminance Lux When we describe the “brightness” of a lit surface we Lux (lx) is the SI unit of measurement for illuminance, are trying to describe the amount of light that emanates and the unit most commonly used outside the US. Lux from it. Luminance is the accepted term for this and is an quantifies the luminous flux within a surface area of 1 expression of the intensity of light emitted by a surface. square meter. 1 lux = 1 lumen per square meter. 10.764 lux It is related to the sensation of viewing a lit surface and, = 1 foot-candle. as such, the measurement relates to the angle of view of the eye looking at the surface. The SI unit (International Illuminance System of Units) for luminance is candela per square Where luminance relates to the light produced by a source meter (cd/2). or reflected by a surface, illuminance describes the light that falls on a surface. We do not see illuminance. What Candela we see is luminance—the light reflected by the surface. The candela (cd) is an SI unit that quantifies luminous The light reflected will be a proportion of the illuminance. intensity in a given direction. Even before the advent A white surface that receives the same illuminance as a of electric light there were attempts to standardize light black surface will reflect more light and have a greater sources, and these were measured against the light of a luminance (or, in visual terms, it will appear brighter). “standard candle.” This early measurement system lingers on in the word “candela,” since one unit is roughly Light meters equivalent to the light of one standard candle. The candle A typical light meter measures illuminance—the light flame radiates light in all directions; the candela also falling on a surface. It provides measurements in foot- relates to the spherical radiance of light. 1 candela = 1 candles (lumens per square foot) or in lux (lumens per lumen per steradian (a conical angle within a sphere). square meter). Illuminance meters are sometimes called A full sphere has a solid angle of 4 π steradians. For a lux meters. To be of use in lighting design, an illuminance light source, such as the standard candle, that produces meter is calibrated to respond to visible light in a similar 1 candela in all directions, this is equivalent to about fashion to the spectral sensitivity of the human visual 12.57 lumens. system. This calibration is standardized and defined by the CIE (Commission Internationale de l’Eclairage or Lumen International Commission on Illumination) photopic The lumen (lm) is an SI unit of luminous flux. It is a sensitivity curve. description of the quantity of light either produced by a As illuminance meters measure the light falling source or received by a surface. 1 lumen is the quantity of on a surface, they tell us little about the luminous luminous flux within a solid angle of this type of steradian intensity of the surface. For this, a luminance meter is emitted by a light source that has a luminous intensity of needed. This type of meter is much less common and 1 candela. much more expensive than an illuminance meter and is rarely used in lighting design. Luminous flux This is a measure of the total amount of light emitted by a light source or received by a lit surface. The SI unit for luminous flux is the lumen. Luminous flux is not a simple measurement of an amount of electromagnetic energy: it is weighted to match the sensitivity of the human visual system to different wavelengths of visible light. Foot-candle The foot-candle (fc) is the unit of measurement used to describe the illuminance of a surface—the amount of light that falls on it. It is not a measure of the luminance of a surface, i.e. how much light is emitted. Instead it is a measure of the illuminance of the surface. Foot-candle quantifies the luminous flux within a surface area of 1 square foot. 1 foot-candle = 1 lumen per square foot. 26 Theory 2. Human factors When designing lighting it is important to understand the physics, physiology, and psychology of how humans sense light, process it, and experience it. This chapter explores how we respond to light, how we adapt to intensity and changes in light levels, and how vision works. Equally important are the psychological aspects of lighting, including mood and cultural preference. Sensing light The human body has many ways of understanding its environment. It has a multitude of specialized systems designed to be sensitive to both internal and external changes. Sound and light are two kinds of stimulus that the body is designed to respond to. They are external stimuli and are transmitted through the environment as waves. Waves can be described in terms of their wavelength (the distance between wave peaks), or by their frequency (the number of wave peaks that pass in a certain period of time). Frequency and wavelength are just different ways of describing the same information about waves. Light is a wave (of electromagnetic energy) that can be described in terms of frequency. Blue light has a frequency of around 660 trillion hertz. However, light is traditionally described in terms of its wavelength rather than its frequency. Blue light is therefore described as having a wavelength of around 470 nanometers (a nanometer is a billionth of a meter). Left For the lighting designer, sight is the principal means by which the end users will interact with his or her work. It is therefore vital for lighting designers to understand something about how the human eye operates and how it responds to light. www.ebook3000.com  Human factors 27 Adaption Receptors are specialized cells that send signals to the A Optic nerve receptors are B The optic system is constantly central nervous system when there are changes in the stimulated by visible light. The trying to adapt to surrounding receptors produce a response that conditions. Given the same body’s internal or external environments. There are is related to the intensity of the stimulus after different lengths of different types of receptor for different functions. For stimulus. With a weak stimulus, time in the dark, the optic nerve example, olfactory receptors respond to the chemical such as a dim light source being receptors fire more frequently as signatures of different odors and trigger our sense of smell, switched on and off, the receptors the system becomes more adapted fire repeatedly for the duration to the darkness. The result is that while taste receptors signal flavor to our brains. of the stimulus. With a strong a light source that seemed weak All receptors act as transducers, converting one stimulus, such as a bright light, the when seen after only 30 seconds form of energy (for example chemical, mechanical, receptors fire more frequently in darkness seems to become or electromagnetic) into another form that is used to —not more strongly. The visual brighter the longer the period system can estimate the relative spent in the dark. Our perception communicate with the brain. Receptors can only be strength of any stimulus by the of the brightness of any light on or off; they have no amplitude or scale of trigger. frequency of receptor signals. stimulus is related to its difference To communicate the intensity of a signal of a received to the background illumination stimulus (such as the volume of a sound), receptors fire and to our level of adaption to the background illumination. more frequently for a strong stimulus and less frequently (Illustrations A and B adapted for a weaker one. from Gregory, Eye and Brain: The If a receptor is stimulated for a prolonged time by the Psychology of Seeing.) same stimulus it begins to decrease its rate of firing, and becomes desensitized to the continuous stimulus. This is called adaption. All receptors display the ability to adapt to a constant stimulus. Walk into a garden and initially the smell of freshly mown grass can be very strong, but it seems to fade even though the smell is still present. When we are adapted to a particular stimulus we only become aware of it again when there is a change: perhaps we go indoors (where we become adapted to the indoor A Weak stimulus environment), then return to the garden and smell the On Off grass anew. Although we are rarely aware of it, the same process of adaption affects our sense of sight. Our visual Response system becomes adapted to the colors in our surroundings when we wear tinted sunglasses, and we are surprised at how different the world looks when we remove them. The process of adaption also allows the visual system Strong stimulus to become more sensitive. In a dark space, we become On Off adjusted to lower light levels over a period of time and the space seems to become brighter. During this process of adaption to darkness, the visual system becomes much Response more sensitive to light, matching its range of sensitivity more closely to the surroundings. B Time spent in darkness 30 minutes 5 minutes 20 minutes 1 hour 0 Time 0.5 seconds 28 Theory Experiencing changes in light levels In our built environment there are many times when we a 40-fc (430-lux) change suggests we will have different encounter rapid changes in the general light level. Moving levels of difficulty in adapting to the changes. Surely a indoors from the bright sunlight of an outdoor space can 40-fc change must be easier to deal with than a 4,000-fc leave our eyes struggling to decipher the interior because one? However, experience tells us this is not the case. of the huge drop in relative light levels. The more time This illustrates an important feature of our visual we spend in this space, the better adjusted (adapted) we system. The rate at which our visual receptors are triggered become to its range of light levels. But if we move from is a roughly logarithmic response to the light intensity. So, what appeared to be a gloomy interior space when we first if you wish an object currently illuminated to 10 fc (108 entered it at midday to a dark nighttime scene, we could lux) to appear to be twice as bright, you need to increase once again struggle initially with the change in light. the light, not by a factor of 2 (to 20 fc/215 lux), but by a Looking at these examples more closely, there is factor of 10 (to 100 fc/1,080 lux). It is very important to something interesting going on that can teach us a remember this when you are trying to control light for great deal about our visual system. The difference in interior spaces, as significant changes in visual brightness illuminance between the sunlit outdoors and the interior require much larger differences in intensity than you may space may be something like 5,000 foot-candles (54,000 otherwise expect. lux) outdoors to 50 fc (538 lux) for a (well-lit) interior—a A single dim light source added to a sunlit room may change of some 4,950 fc (53,460 lux). Moving from this make no noticeable difference to the total illumination. interior into a night scene illuminated only by street However, if the same dim light source is added to a lights may be a move between 50 fc (538 lux) and 0.5 fc windowless room that contains only one other, dim, light (5.4 lux)—a change of only 49.5 fc (532 lux). On paper, source it can make a very noticeable difference. the disparity between a 4,000-fc (43,000-lux) change and Right The optic nerve receptors do not have a simple 1:1 relationship between the strength of the stimulus and frequency of firing. Instead, the rate of firing has an approximately logarithmic relationship with the stimulus. It will take a ten times increase in stimulus brightness to produce twice as many signals. (Illustration Relative intensity adapted from Gregory, Eye and of stimulus Brain: The Psychology of Seeing.) 1 10 1,000 www.ebook3000.com  Human factors 29 Eyes and the sense of sight Plants create their own food, relying on chlorophyll, The human eye contains around 120 million a photosensitive chemical that changes composition receptors, but they are not evenly distributed over the on exposure to light. Chlorophyll absorbs the light retina. There is one small central part where receptors and provides energy for the process of photosynthesis. are very tightly packed. This densely packed area—the Similarly, our sight, and the sight of all seeing animals, fovea—only makes up a tiny part of the surface area of the relies on a photo pigment. Rhodopsin is a purplish red retina and covers only around 1.5 degrees of our field of pigment contained in the receptor cells in the retina, and view, yet it provides the most detailed part of our vision. its light-reactive qualities have been harnessed to provide Animals whose natural habitat is plains and open country the sense of sight by converting the light into a chemical have foveae that are elliptical, stretched horizontally to signal to the brain. encompass their surroundings. In contrast, humans have To resolve fine detail, a lot of light must be gathered. roughly circular foveae that match the eyes of forest- In turn, this requires quite a large eye. Humans have dwelling animals. Our visual system has evolved to deal much larger and more sophisticated eyes than most with the visual complexity of an environment where it animals, and sight is one of our most acute senses. The was necessary to locate food and danger both horizontally limiting factor in the resolution of an eye is the number and vertically. of receptors available to capture the incoming light. Human eyes have around 200,000 receptors per square millimeter. By comparison, a hawk may have around 1 million receptors in the same area, which give it its unparalleled ability to identify tiny prey animals from distances far beyond the reach of human vision. Pupil Left Iris Aqueous humor The human eye is an amazing vision centered at the fovea; low Cornea confluence of features that collect light sensitivity restricted to the the light energy that our visual less “high resolution” parts of Ciliary system uses to give us our sense the retina; a limited range of iris muscle Conjunctiva of sight. The muscular contraction aperture (which means a limited of the iris gives some control over range of attenuation of bright the amount of light that can enter light); light-sensitive receptor cells the eye, becoming small in very positioned behind a net of blood bright conditions and opening vessels; and an actual hole—a up to gather more light in dim blind spot—in the visual image conditions. The curve of the front where the optic nerve exits the Crystalline of the eye and the shape of the back of the eye. Luckily, the visual Vitreous humor lens crystalline lens allows a focused system can perform remarkable image to be created on the retina compensations that extend the at the back of the eye. Muscles sensitivity range beyond the Blind spot around the lens can alter its shape physical constraints of the iris. It to bring close or distant objects can produce a full color image into focus. Light hitting the retina over the whole of our field of view stimulates light-sensitive receptor and can even seamlessly fill in our cells that produce electrical signals, blind spot. The eye is an amazing Retina which are sent to the visual optical device, but much of the cortex in the brain. And yet, as magic of vision happens after light Fovea a piece of design, the eye is far reaches the retina. from perfect. Limitations include Optic nerve a restricted area of sharp color 30 Theory Stereo vision Humans, like other hunting animals, have eyes that are mounted close together on the front of the head, giving a focused, forward-looking view. A large horizontal overlap of around 120 degrees out of a field of view of around 180 degrees gives us acute vision in this main portion of what we can see. The overlapping field of view combined with the spacing between our eyes means our brains receive two slightly different views of a scene, each one offset by the distance between our eyes. Our brain combines the information from the two images and gives us stereo vision—the capacity to accurately estimate the three- dimensional location of an object just by looking at it. Try looking at an object in the foreground, then shut each eye one at a time. Distant objects will not move much, but one that is close to us will appear to jump significantly between the two views when seen relative to the background. The amount of displacement between the two images is proportional to the distance between our eyes and the object. Our brains can quickly process and decipher this information, to precisely plot the location of objects in three-dimensional space. Stereo vision allows us to accurately pick up objects, or climb and leap onto and over tree branches, and gives us depth perception. Other optical stimuli can suggest depth without the need for two views. These include overlapping objects, scale, foreshortening, and aerial perspective, and are devices employed by painters to give a three-dimensional impression on a two-dimensional surface. An experienced designer can take advantage of these visual cues and use light to manipulate and enhance our visual response to space. 0° Right 0° 80° 30 Our eyes are mobile and have a 33 ° 70° wide potential field of view, but how the eyes are placed within 60° the head restricts how far we can 50° 0° see in any direction. The view 60 30 40° ° from each eye is restricted laterally by the nose and vertically by the 30° brow and cheekbone. When the 20° view from each eye is combined, 10° we get a field of view like this diagram. The dark areas at the top 270° 90° and bottom are where the brow and cheeks obstruct the view. The clear area in the center is where the coverage of the two eyes overlaps and gives stereo vision. The hatched area is where vision 24 0° 12 0° comes from only one eye because of occlusion by the nose. 21 0° 0° 15 180° www.ebook3000.com  Human factors 31 Left Arrangement of a virtual model illustrating stereo vision. If two cameras (or eyes) are spaced some distance apart and aimed in the same direction, the view each sees will be slightly different. Below left The view from the left-hand camera. Below right The view from the right-hand 55 in camera. Note that the colored columns obscure the background scale in different locations in each