Lighting Lecture 2 Notes PDF

30.09.2024 LIGHTING Assist. Prof. Bilge ŞAN ÖZBİLEN Sept 2024 Lecture 2 Light Electromagnetic Radiation  30.09.2024 300 000 km/s...

30.09.2024 LIGHTING Assist. Prof. Bilge ŞAN ÖZBİLEN Sept 2024 Lecture 2 Light Electromagnetic Radiation  30.09.2024 300 000 km/s LIGHT is the visible spectrum – that part of the spectrum of electromagnetic energy that excites our neurological visual system that enables us to see. Light is a small segment of the electromagnetic radiation spectrum; visually evaluated energy A continuous spectrum white light can be split by a prism into its components, which are perceived as colours, which means white light is the total of all color lights like red orange yellow…blue Colour Wavelength band (nm) Red 780–630 Orange 630–600 Yellow 600–570 Green/yellow 570–550 Green 550–520 Blue/green 520–500 Blue 500–450 Violet 450–380  30.09.2024 If the spectrum of a light has all colors (wavelenghts) almost at same energy this means it is a good source of white light. The light which contains all light radiations (380-760 nm) in an equal energy is called Hypothetic white light But no natural or artificial light source has the feature of equal energy spectrum. CIE standard illuminant D65 is intended to represent average daylight and has a correlated colour temperature of approximately 6500 K. D65 should be used in all colorimetric calculations requiring representative daylight, unless there are specific reasons for using a different illuminant. Variations in the relative spectral power distribution of daylight are known to occur, particularly in the ultraviolet spectral region, as a function of season, time of day, and geographic location. Spectral power distribution of D65 (CIE): International Commission on Illumination Ref: Dr. Esra Sakınç Lecture Notes 1000K° red Color of light 2000-3000K° yellow 4000K° white  Similarity with daylight 6000K° blue Below 3300 K - hot Color Temperature 3300 K - 5300 K - middle Above 5300 K - cold  30.09.2024 Color temperature  Similarity with daylight  30.09.2024 Monochromatic Light Narrow band spectrum The hue of light changes according to the monochromatic radiation energies in its spectrum. Monochromatic light refers to light that is of one color. Since it only emits one color, monochromatic light has a single wavelength. Wavelengths are seen as a rainbow of colors when light is passed through a spectrum. Therefore, monochromatic light would emit just one of these colors. The colour of light depends on the source (the spectral composition of the emission), but can also be produced by filters. Ref: Dr. Esra Sakınç Lecture Notes RGB Red, green, blue The three-colour theory of light distinguishes red, green and blue as the primary colours, and any colour can be defined in terms of its redness, greenness and blueness Red + green=magenta. Green + blue=cyan. Red + green=yellow. White light may be obtained by blending them in equal quantities. Red + green + blue=white, the whole spectrum. Color on television and monitors is produced by three color "guns" corresponding to each additive primary. These produce color intensity based on a voltage level, from 0 to 255. Obviously, 0, 0, and 0 will produce black, or absence of color, and 255, 255 and 255 will produce white. Other colors correspond to a specific voltage combination. Multiple 255 times 255 times 255 and how many color combinations do you get? More than 16.7 million, presuming your monitor is capable of showing that many (most modern monitors are capable of this 24-bit, or "true color"). https://www.ndsu.edu/pubweb/~rcollins/242photojournalism/colortheory.html Ref: Dr. Esra Sakınç Lecture Notes  30.09.2024 Vision The light that comes to eye turn to neural stimulation by optic nerves and sent to brain. Then brain analyze these electrical signals and determines what the object is. Vision Rodes and Cones The retina contains a large number of light receptors, called, because of their shape rodes and cones The cones perform precise seeing at normal brightness levels and provides colour perception. The rodes are extremely light-sensitive; as Rod cells – shape a result they function well only st low levels Cone cells- color of night. Day vision is called photopic vision and night vision is called scotopic vision  30.09.2024 Visual Perception Parameters Ref: Dr. Esra Sakınç Lecture Notes Reflection / Transmission + Absorption  Human perceive objects because they absorb, reflect, transmit light that comes on them according their surface properties which makes them visible as they are. Light is absorbed , reflected and transmitted by transparent and translucent surfaces a+r+t=1 Light is absorbed and reflected by opaque surfaces a+ r = 1 a= light absorption coefficient of a surface (%) r= light reflection coefficient of a surface (%) t= light transmission coefficient of a surface (%)  30.09.2024 Reflection / Transmission + Absorption HOW MUCH LIGHT IS REFLECTED ? White, light greys and all Light colors (like pink, baby blue) reflect more light Black, dark greys and all Dark colors (like dark purple, red, blue) reflect less light Amount of light reflected is not a factor of being matte or glossy Ref: Dr. Esra Sakınç Lecture Notes Reflection / Transmission + Absorption HOW MUCH LIGHT IS TRANSMITTED ? Ref: Dr. Esra Sakınç Lecture Notes  30.09.2024 HOW THE LIGHT IS REFLECTED ? HOW THE LIGHT IS TRANSMITED ? One direction Reflected objects are visible but not the surface itself, therefore they are not visible. every direction Light reflects from any point to any direction. Eye at any point receives light from every point and every point of surface are visible Ref: Dr. Esra Sakınç Lecture Notes How do we see the objects colorful?  30.09.2024 Surface color = Light coming to the surface x Color properties of surface (properties of light that comes to eye) (light spectrum) (reflection spectrum / transmission spectrum) Ref: Dr. Esra Sakınç Lecture Notes  True Color The perceived color of the surface while surface is enlightened by an achromatic (white) light in equal energy spectrum.  Seen Color The perceived color when the surface is enlightened by colored (chromatic) light. Ref: Dr. Esra Sakınç Lecture Notes  30.09.2024 Direction of Light & Shadows  Direct Light  Diffuse Light  Direct+Diffuse Light Direction of Light & Shadows https://www.balchagi.net/part/?pageid=1&mod=document&kboard_id=48&view_iframe=1&uid=1317  30.09.2024 LIGHT SOURCES They are elements that convert electrical energy into light radiations. Production Geometric Shape Origin Distribution light sources that emit Primary Point Natural Isotropic energy equally in all directions Secondary Linear Artificial Anisotropic Surface PHOTOMETRIC UNITS Luminous Flux (Işık Akısı)  Luminous energy emitted by a light source, Ф (lumen, lm) (Aydınlık Düzeyi) Illumination Level  The quotient of the flux divided by the area of the surface, E (lm/m2, lux)  The density of luminous flux incident on a surface (cd/m2) Typical illuminance levels on different surfaces under the noonday sun in temperate climates  30.09.2024 PHOTOMETRIC UNITS Luminous Intensity (Işık Şiddeti)  Luminous flux per unit solid angle in a given direction, I (candela, cd) Luminance (Parıltı)  The luminous intensity of any surface in a given direction per unit of projected area of the surface as viewed from that direction, L (cd / m2) Ref: Dr. Esra Sakınç Lecture Notes  30.09.2024 Luminance Luminous Efficacy (Işık Etkinliği) The Illuminating Engineering Society of North America (IESNA) defines lamp efficacy as “the quotient of the total luminous flux emitted divided by the total lamp power input.” It is denoted by e and expressed in lumens per watt (lm/W). e= Φ / P (lm /W) Φ : total luminous flux (lm) P : power (W)  Etkinlik faktörünün (ışık etkinliği/verimliliği) büyük olması  30.09.2024 Glare (kamaşma) is an interference with visual perception caused by an uncomfortably bright light source or reflection Source: CIBSE Guide KS06 Comfort  Discomfort glare  Disability glare Luminance distribution disorder  Difference between the lowest and the highest luminance Glossy reflections Flicker  From screens, bright surfaces rapid or quick and repeated changes in the brightness of light over time  30.09.2024 Color rendering of light (Ra) (Color rendering index) (CRI) (Renksel Geriverim) Especially when it is important to see the true colors of the objects the color rendering of the light source have to be high. Class 1A color rendering indicates the effect of a light source on the visible colors of objects illuminated by the light source. It is obtained by comparing a surface color in two situations, the visible color illuminated under a given light and the visible color illuminated by a reference light. Visual Comfort  Illuminance Level Psychological  Luminance distribution Physiological  Color  Contrast sensitivity  Visual accuracy  Speed of vision  30.09.2024 Educational buildings Classrooms, 300 19 80 Lighting should tutorial be controllable Visual Comfort rooms Classrooms 500 19 80 Lighting should for evening be controllable classes and adults  Illuminance level (E) education Lecture hall 500 19 80 Lighting should be controllable  Glare index (UGR) Blackboard 500 19 80 Prevent specular reflections  Uniformity (U) luxmeter Art rooms 500 19 80 Art rooms in 750 19 90 TCP >= 5000K art schools  Color rendering (Ra) Technical 750 16 80 drawing rooms TS EN 12464  30.09.2024 PHOTOMETRIC LAWS ABNEY LAW ΣE = E1+E2+E3+………En If light comes from more than one light source at a point A, the illuminance levels at that point can be summed. E2 E3 E1 PHOTOMETRIC LAWS INVERSE SQUARE LAW If a point source creates an Iα luminous intensity in the direction of α, the illuminance levels on surfaces that are perpendicular to this direction are inversely proportional to the square of their distances to the source.  30.09.2024 PHOTOMETRIC LAWS COSINE LAW The illuminance of a surface S in a parallel beam light is a function of the angle between the normal to the surface and the light beam. α En Es Es = En x cos α PHOTOMETRIC LAWS LAMBERT’S LAW  If the luminance of a luminous surface (i.e. a surface which emits light) is equal in all directions, this surface is called a «Lambertian» surface.  For Lambertian surfaces Lα = L = Constant Ф=πxLxS Here, Ф [lm]: the total luminous flux of the surface in lumens, L [cd/m2 ]: the constant luminance for the Lambertian surface S [m2 ] : the surface area