Week 1 Lighting Fundamentals PDF

Week 1. LIGHTING FUNDAMENTALS. PART 1 BASIC PRINCIPLES LIGHT DIRECTION SHA...

Week 1. LIGHTING FUNDAMENTALS. PART 1 BASIC PRINCIPLES LIGHT DIRECTION SHADOWS 1. BASIC PRINCIPLES VISUAL TECHNOLOGIES 1.1 LIGHT BEHAVIOUR A white ball on a white ground demonstrates how light behaves in different everyday situations (illustrates a sunny afternoon). The main source of light is the sun, while the blue sky - a second source of light with very different characteristics. Some bounced light between the white base and the ball supplies a third source of light. The brightest light is coming from the sun and is white light emanating from a small source, which causes it to cast sharp-edged shadows. The second source, the blue sky, is a very large light source, creates very soft shadows (which are completely masked by the direct light coming from the sun). The smaller the source of the light, the harder the shadows. The light coming from the blue sky has a very strong colour cast, which affects everything in this scene. The shadow cast by the ball is blue because it is illuminated by blue skylight, since the ball is shielding it from the white light of the sun. Those parts of the ball not in direct sunlight also take on a blue hue because they are lit by the blue sky. The light that is reflected between the card and the ball is also predominantly blue (even though the card and ball are white), since it is blue skylight that is being reflected by the white objects. The surfaces that are closer together receive more of this reflected light than those that are further apart. The darkest areas in the image are the base of the cast shadow and the border between the areas of the ball that are in sunlight and in shade: this zone is called the terminator. The base of the cast shadow is very dark because it receives no sunlight and the ball is masking it from most of the skylight and bounced light. The other end of the cast shadow is lighter because it is receiving more light from the sky as well as bounced light from the ball. Page 1 of 9 1. 2. TERMINATOR The terminator is the darkest area on the ball. This is partly because of the effect of contrast – being so near to the very bright side of the ball in sunlight makes it appear to be darker – but it is also receiving less of the bounced light reflected by the white card. So, unlike the rest of the ball, which is receiving either full sunlight or light reflected from the white card, its main source of illumination is the blue sky. A terminator is the area in between the main light (the sun) and the fill light (the reflected light from the card). 1.3 SUNLIGHT Why is the light from the sky blue? Visible light is made up of particles of pure energy called photons, which have different wavelengths depending on their colour: blue light comprises photons with shorter wavelengths, whereas red light is made up of photons with longer wavelengths. White light from the sun is composed of a continuous spectrum of colours, conventionally divided into the colours of the rainbow (with progressively longer wavelengths: violet, indigo, blue, green, yellow, orange and red). It is the mixture of these colours that produces white. 1.4 DIFFUSE SCATTERING When light travels through the atmosphere of the earth, the shorter wavelengths of light become scattered. The earth’s atmosphere is composed of various gases, and these gases scatter light. Photons travelling through the atmosphere encounter electrons, which can absorb and re-emit them and point them in a different direction, causing a diffuse scattering effect. Page 2 of 9  Shorter wavelengths are more likely than longer ones to be diffused, so the photons scattered in all directions by this interaction are predominantly blue. Longer wavelengths of light, such as red, can travel further through the atmosphere without being scattered. 1.5 RADIANCE / BOUNCE LIGHT When light hits a surface it either bounces or is absorbed by it, depending on the colour of the surface. A white object will reflect all wavelengths equally, whereas a black object will absorb them all. When white light hits a red surface the blue and green wavelengths are absorbed and the red light is reflected. So, if white light hits a red surface the photons reflected by the surface will be red. When these photons hit the next surface in their path they will therefore illuminate it with red light. This phenomenon is known as radiance (bounce light), and causes the colours of adjacent objects to influence each other. Radiance is usually a subtle effect, and it takes a great deal of light for it to become apparent. In soft or dim light it may not be visible at all, but in bright light it can add a lot of colour to the surfaces it affects. Light reflecting between objects of the same colour can create a very saturated effect – the bounced light reinforces the existing colour of the underlying surface, making it glow vividly. 1.6 WHITE BALANCE Most light sources in everyday situations have a colour cast, although the brain is very good at filtering this out. As long as there is a vague mixture of the three primaries in the light, the brain interprets it as white. Even under lighting with very strong colour we can filter the information our eyes receive and make sense of the colours so that we perceive them in a relative manner rather than an absolute one. Page 3 of 9  The obvious way of demonstrating this is to use a digital camera with the white balance set to daylight: this is a neutral setting, which will reflect the colours that are actually there. The brain will convert the colours to make them resemble the first picture, top image, but the camera paints the true picture, bottom image. An easy way to confirm this fact is to look at windows from the outside: next time you are outdoors in the evening look at the colour coming from the windows of houses and you will see that the house interiors are bright orange. When we aren’t directly under the light source, we can see its true colour. Something very similar happens when we stand in open shade, where the light is very blue. We perceive the light as being neutral, but if we step back and look at the shade from under sunlight, the blue cast is much easier to see. There are many other situations where lights have a strong cast: fluorescent light is often green, street lighting is very deep orange, evening sunlight progresses from a light yellow to a deep red, and so on. 2. LIGHT DIRECTION 2.1 THREE-POINT LIGHTING A commonly taught lighting technique is the classic three-point lighting set- up. Three-point lighting was originally developed as a way of lighting for film. It consists of a bright main light coming from one side, dim fill light coming from the opposite side, and a back light behind the subject, which is used to pick out edges and highlight form. Page 4 of 9  Key or Main Light : The Key Light creates the subject’s main illumination, and defines the most visible lighting and shadows. The Key Light represents the dominant light source, such as the sun, a window, or ceiling light. Fill Light: The Fill Light softens and extends the illumination provided by the key light, and makes more of the subject visible. Fill Light can simulate light from the sky (other than the sun), secondary light sources such as table lamps, or reflected and bounced light in your scene. Rim or Back Light: The Rim Light (also called Hair Light, Shoulder Light) creates a bright line around the edge of the object, to help visually separate the object from the background and highlighting contours. FRONT LIGHTING Front lighting is where the light source is directly behind the observer’s point of view. Front lighting does little to reveal form or texture since any shadows are mostly hidden from view, and as a result it can make things look flat. However, soft, diffuse frontal lighting can be flattering to some subjects for this very reason – it can help conceal wrinkles and blemishes, so it is quite often used in portrait and product photography. A drawback of using front lighting is that areas of an image can look washed out. SIDE LIGHTING Side lighting is very good for showing form and texture and lends a three-dimensional quality to objects. Shadows are prominent and, as a result, contrast can be high. You can use side lighting to throw dramatic shadows onto surfaces such as walls to create atmosphere. Side lighting is generally attractive and is often used to great effect: it is the type of lighting encountered at the beginning and the end of the day and, as such, is Page 5 of 9 often seen in films and photographs. Some potential drawbacks of using side lighting are that areas of an image can be lost in shadow and imperfections and wrinkles can be revealed. BACK LIGHTING Back lighting is where the viewer is looking into the light source, and objects will have their lit sides facing away from us, so that they are either silhouetted or darkly lit by the fill light. It is usually a high-contrast situation and can often look very atmospheric and dramatic. If the light source is at a slight angle relative to your point of view, objects will have a rim of light defining one or more of their edges. The harder the light the more pronounced this rim will be. Back-lit scenes usually contain a lot of shadow unless the light source is very soft. The rim lighting that occurs can be very useful for defining forms among the shadows. Another feature of this kind of light is that it reveals transparency, translucency and any fine detail or texture along rim-lit edges. TOP LIGHTING Top lighting is a slightly more unusual situation, although it is common in overcast daylight. It can also be encountered in sunshine at midday, in some interiors and in other situations, such as stage lighting. In soft light it is an effective way of showing form. Under hard light it can lend an air of mystery by casting dramatic shadows that conceal most of the forms beneath them – people directly beneath hard lights will have black holes for eyes since their eye sockets will be in total shadow. For overcast daylight it is the most realistic setup, with the whole sky acting as a large diffuse light source. It’s also an unusual lighting solution for more atmospheric situations, and the very fact that it’s not often seen can be used to create an uncomfortable feeling. BOTTOM LIGHTING If lighting from directly above is rare, then lighting from directly below is even more unusual. In a natural context this might happen if you were standing over a campfire, or holding a torch. Reflected light can also come from below – from water, for instance. It lends a strange appearance to even the most familiar things, since what is usually seen in light and shade will be reversed (think of a person shining a torch onto his face from below: the shadows appear to be upside down). Again, the very rarity of this kind of lighting can be used to creative effect. We instinctively recognize when things don’t look right, and you can use this to create specific moods by changing lighting to convey different emotions and provoke responses. Page 6 of 9  3. SHADOWS 3.1 SHADOW TYPES There are two kinds of shadow: form and cast. Form shadows are the shaded areas on a surface where a light source cannot reach. Cast shadows are what we typically think of as shadows: the shadows projected by an object onto a surface (such as the ground) when the object comes between the light source and the surface. Shadow plays an important role in your artwork, giving it solidity and form as well as creating drama and suspense. 3.2 SECONDARY LIGHT Shadows are, in most cases, filled with some secondary light, and generally more of this secondary light will illuminate form shadows as opposed to cast shadows. When light bounces off a large area, such as the ground, the reflected light is effectively coming from a large and therefore bright source. This means that the form shadow on the sphere is getting quite a lot of fill light coming from the ground, as well as light coming from the atmosphere. Because the sphere itself is much smaller than the ground, it reflects less light. The cast shadow therefore gets only a small amount of fill lightfrom the sphere, and is mostly lit by the atmosphere. Notice also that the terminator is dark and saturated. 3.3 COLOUR IN SHADOWS Shadows are themselves illuminated by what is known as fill light, usually a secondary or reflected light source. In the vast majority of cases fill light will be coming from a soft and diffuse source, such as light reflected from a wall or the ground, or from skylight. This means that even in harsh sunlight, the shadow side of a form will be lit by diffuse light. Shadows are rarely black, but will generally contain some light and colour, which tends to be soft and muted. Page 7 of 9 It is important to realize that there is often a lot of colour found in shadows, be it strongly coloured light from the sky, an optical effect, or light scattered through skin or some other translucent material, and all of these colours have strong impact on the quality of your image. 3.4 FORM SHADOW Form shadows give objects depth, especially with side lighting, and really help to convey the form of an object. The absence of form shadow is why frontal lighting can look so flat. Form shadow also reveals texture. These 3D renders of a tree trunk illustrate these points: the second image has more depth, and the trunk looks more solid and dimensional. The texture is also greatly emphasized by the stronger, more directional light. Thus the form shadow plays a very important role in conveying both the form and the texture of an object. 3.5 AMBIENT OCCLUSION In 3D rendering another layer of realism can be added to rendered images by creating an ambient occlusion pass. This is created by darkening surfaces that are adjacent to others, and creating a shadow around the area where they meet, simulating the effect of a large, diffuse light source. The technique creates a sense of depth and solidity, illustrating perfectly how shadows contribute to the illusion of depth and form. In diffuse lighting this is the main way we have of reading forms: as objects get closer to each other, less light is available from the environment and so the surfaces darken. It is also worth noting how the more obstacles there are in the path of the environmental light, the darker the shadows become. 3.6 LIGHT SOURCE The most important factor in determining the appearance of shadows is the size and distance of the light source: a small or distant light will cast hard-edged shadows, whereas a large or adjacent light will cast soft-edged shadows. The reason for this is that the rays of light cast by the small or distant light will be more or less parallel, but in the case of the large and adjacent light there will be considerable overlap of the light rays. Page 8 of 9 3.7 LIGHT SIZE & PROXIMITY With a small or distant light source, the rays of light have little or no overlap, giving the shadow a crisply defined hard edge. The darkest part of the shadow, known as the umbra, covers most of the area and the lighter, softer part of the shadow (known as the penumbra) is found only at the far fringe. The penumbra increases in area as it gets further away from the shadowcasting object. However, with a large adjacent light source there is far more overlap of the light rays, which results in a shadow with a much softer edge. In this case, the umbra becomes much more prominent, as the edge is being filled by overlapping rays from the larger light, and it is the penumbra that is less prominent. The larger the light and the closer it is to the object, the softer the shadow becomes. EXAMPLES OF LIGHTING: Page 9 of 9