Lighting Principles

Lighting §

• Consider that light not only comes from the main light source (i.e., sunlight or a spotlight) but also from light reflected off of other objects in the scene (see here).

  • When light is reflected from to , it not only adds light to but it also adds some of the hue of onto .
  • General Principles of Reflected light
    • In shadows, up-facing planes are cool and downfacing planes are warm.
    • Reflected light falls off following the inverse square law. Thus, it falls off rapidly.
    • The effect of reflected light is more apparent when all other sources of reflected light and fill light are removed.
    • The color of a shadow is the sum of all the sources of reflected illumination.

• Remember that the brightness of any point source illumination diminishes following the inverse square law.

• Hard Light comes from a sharp, small point.

  • It tends to be more directional and more dramatic.
  • It produces crisper shadows.
  • It brings out more surface textures and highlights.

• Soft Light comes from a more diffuse source.

  • It tends to be more easy on the eyes.
  • It reduces the confusion of cast shadows.
  • It reduces the contrast between light and shadow. Objects tend to transition between the two in a more gradual manner.

• Diffusing light through a material or passing it through translucent material makes it softer..

• Luminescence — light emitted at cool temperatures, tends to follow the following principles.

  • They often graduate from one hue to another.
  • Blue-green colors are the most common in the ocean because those wavelengths travel the farthest through water.
  • Paint the scene darker first then add luminescence and glowing effects.

• You can use lighting, in particular, lighting from occluded objects, to add intrigue and guide the viewer’s eyes.

• Lighting affects the value and can make dark tones appear brighter than lighter tones.

Lighting Techniques §

• Consider the lighting ratio — the tonal separation between light and shadow. Softer lighting reduces the lighting ratio; Harder Lighting increases it..

• Most portraits are painted in Three Quarter Lighting where light comes from in front of the model. This illuminates the majority of the model.

• Rembrandt Lighting involves arranging the light so that the nose shadow merges with the side of the face.

  • This results in a lighted triangle on the cheek closest the viewer.
  • The triangle should be no longer than the nose and no wider than the eye.

• Frontal Lighting involves light shining directly towards the model from the viewer’s perspective.

  • In this case, very little shadow is visible.
  • It emphasizes local color or pattern.
  • It creates apparent outlines — which are simply the fringes of shadows appearing at the edge of a form.

• Edge Lighting comes from behind to touch the sides of the form.

  • It requires a strong light source directed towards the viewer.
  • It creates apparent highlights — blobs of lighter regions appearing at or along the edge of a form.

• Contre-Jour is a form of backlighting where the subject blocks the light.

  • The light surrounds the object’s edges.
  • It makes the silhouette of the form more apparent while muting some of the details.
  • The regions of light are not pure white. They diffuse slightly.

• Light from Below is associated with underlighting or theatrical footlights. It rarely occurs in nature.

  • It grabs the viewer’s attention.
  • It suggests a magical, sinister or dramatic feeling.
  • It can make the familiar appear unfamiliar since we usually see things with the light shining from above.
  • It can make an object look bigger if only parts of it are lit from below by small weak lights.

• Spotlighting involves shining a spotlight on an object.

  • The spotlight allows the viewer to focus on a part of the image by placing it in bright light and placing the rest in shadow.
  • Shadows as a result of the spotlight being occluded should match the ambient light.

Form §

Lighting on a Sphere. Image taken from Briggs (2007) http://www.huevaluechroma.com/022.php

• The terminator is the area where the form transitions from light to shadow.

  • Geometrically, it is where light rays from the source are tangent to the edge of the form.
  • If the light is soft, the transition at the terminator will be more gradual
  • The form’s shadow begins beyond the terminator.

• The core shadow only forms if the secondary source of light doesn’t overlap too much with the main light.

  • Adding the core to the piece gives the form more impact.

• Texture is difficult to see in the shadow. It is much more visible in fully lit areas, especially in the half light region

• In soft light, there is no distinct light, shadow, terminator or core. Lighting depends on which sides are facing the source of diffused light.

• A Shadow is formed when an object occludes light.

  • Shadows suggest depth.
  • Shadow is not pure darkness. Other sources of light will modify the shadow.
    • Reflected light raises the tone of the shadow.
    • The darkest part of the shadow is at the point of contact.
  • The edge of a shadow gets softer as the distance increases from the object that casts the shadow.
  • Dark accents occur at places where forms come close enough to each other. This leaves a dense area of shadow called a Crevice Shadow / Occlusion Shadow
    • Common in cases where materials push together in folds or at points of contact with the ground.

• One way to create drama and visual interest (esp. in a vertical form) is to have the top be in light and the rest in shadow.

• Not all material can be decomposed into form and subsequently lit. Consider materials that respond differently to light. Typically this involves variations in the material’s density or composition

Surfaces §

• Subsurface Scattering is a phenomenon where light spreads out beneath a surface to create a slight glow.

  • It affects forms with depth.
  • It shows up most strikingly when the following are met:
    • The material is translucent.
    • The object is small
    • There is backlighting.
  • Flesh / Skin is also subject to subsurface scattering. Such scattering gives it a slight red glow with sufficient backlighting.

• Consider how light affects the face:

  • The forehead tends to have a lighter color since it has less muscles and capillaries.
  • The center of the face (including the ears, nose, and cheeks) are redder because they have more capillaries.
  • The lower part of the face has slightly deoxygenated blood due to less capillaries (hence it is rendered blue / green-ish by some artists.)

• Keep masses of surfaces simple (for example, simplify the forms of hair or foliage.)

  • Use softer edges to reduce the distinction between hair strands.
  • Highlights go across, not along, curving shapes.

• Consider surfaces that act like lenses and focus light rays onto spots or lines of light.

  • They produce Caustics, wavy bands of light projected onto a surface either through reflection or refraction.
  • The shape of the caustic is determined by the curvature of the reflective surface.
  • Caustic effects are apparent when light shines through curving glass (refraction) or reflects off a surface.

• A Specular Reflection is a reflection of an image of whatever is around the surface.

  • This happens when the object is shiny (highly reflective). It reflects images of adjacent objects.
  • Consider the following rules for specularity.
    • More reflective surfaces imply a broader range of values needed to paint it/
    • Convex reflective surfaces reflect a miniature view of the scene around the object.
    • Treat specular patterns as extra layers on top of usual factors for lighting .

• A highlight is a specular reflection of the light source on a wet or shiny surface.

  • The highlight on any glossy form is not pure white. Instead, it is the combination of the color of the source and the local color of the object.
  • Annular Highlights are highlights that form on small patches of the object. This happens when light illuminates only a few patches of the object.
    • These have a role in orienting the viewer towards the light source .
  • Only surfaces perpendicular to the direction of the light catch the highlight.

• A Color Corona is a band of colorful light which surrounds an extremely bright light source.

  • Also called lens flare.
  • It happens due to the scattering of light as a result of particles in the atmosphere.
  • The glow of the color corona takes on the native color of the source.
  • A color corona can make a source seem brighter than white

• Motion Blur pertains to a form of blurring where a form moves rapidly in front of an observer camera.

  • Motion blur helps imply a motion.
  • The faster a form is moving, the more it is blurred.
  • The blur is greatest in relation to the path of the moving object.
  • Only edges perpendicular to the movement are blurred.

• Speed Blur pertains to a form of blurring where a camera tracks along a fast moving object.

  • The whole background blurs radially from the vanishing point along the path of the movement .

Atmosphere §

• The sky is blue due to Rayleigh Scattering where air molecules refract shorter wavelengths of light.

  • The general principle is that the farther light has to travel through the atmosphere, the more blue wavelengths are scattered which means a bluer hue in regions where the lights scatters.

• The sky is not a flat even blue. The sky has a gradient based on two factors.

  • Solar Glare - based on the proximity of the sun.
    • The value of the sky darkens as we move horizontally away from the sun.
  • Horizon Glow - based on the angle above the horizon with which it is viewed.
    • As we move from the zenith to the horizon, the sky tends to be lighter because we are looking through more atmosphere.
    • The darkest deepest blue point of the sky, called the well of the sky is at the zenith only at sunrise and sunset.

• As we approach the sun, the sky color gets lighter and warmer due to the volume of light being scattered.

• The color of the clouds depends on their size and their position relative to the sun

  • Clouds closer to the sun have dark centers and light edges.
  • Clouds in front of the sun are lightest at the top or center and darker at the edges.
  • Smaller clouds appear less white than larger clouds due to reflecting less light.
  • Light hitting the tops of clouds remain relatively white compared to the light closer to the ground. Higher clouds receive more light.
  • Remember that clouds can cast shadows which make the light less uniformly distributed.
    • The margin between light and shadow must be a soft edge. The transition between full light and full shadow is large.
    • The shadows match the clouds visible in the sky.
    • The shadow is darker and cooler but not as dark as shadows cast directly by the sun. This is because the light in the shadow area is the average of blue light and diffused white light.

• Atmospheric Perspective - the way objects are perceived changes as they are viewed through a distance through layers of illuminated sky.

  • The farther we move, the more the color of the object appears to match the color of the sky.
  • Darkest areas are affected first, generally shifting towards light blue.
  • The illuminated sides of objects generally lose saturation and become grayer as they move farther away. Warm colors also become cooler.
  • Distant details appear blurry. Contrast decreases.
  • Bright white objects in the distance become warmer in color (red-orange).
  • It only happens when the air is illuminated.
  • This effect is enhanced by dust, moisture, haze or smog.
  • The general rule: Warm colors advance, cool colors recede

• Reverse Atmospheric Perspective - happens in certain cases where as we move farther, the scene appears to get warmer

  • It happens when there are more air particles near the sun, especially at sunrise or sunset. The particles scatter the orange-colored sunlight.
  • There is an apparent orange halo surrounding the sun.
  • The phenomenon, then, is due to light spilling from the refracted sunlight.
  • It tends to convey a feeling of strangeness and excitement.

• The exact hue at the horizon depends on the time of day (ranging from pale cerulean to warm gray to dull orange).

  • Colors become bolder and more dramatic at dusk and dawn, when the sun is at its peak
  • When the sun is low, sunlight travels through more miles of atmosphere which scatters more blue light.
  • When the sun sets, we observe a red-orange glow in the sky at the spot nearest where the sun crosses the horizon.
    • Another glow comes directly opposite the sun. From this antisolar region, a gray layer rises (it’s the Earth’s shadow).

• In extreme foggy conditions, light cannot penetrate the fog so light will appear to come from all directions.

  • If sunlight does penetrate, shadows will be lighter due to the “softness” caused by the fog.
  • Rainbows can form due to the refraction of white light caused by particulates. However, rainbows are not geographic. Their geometry is dependent on the viewing angle.
    • A secondary rainbow can form as a result of light refracting a second time.
    • In between the primary and secondary rainbow is a region called Alexander’s Band which makes the atmosphere in this region appear slightly darker.
    • The colors of the rainbow are always lighter than the background. The colored light of the rainbow is added to the light in the scene behind it .

• Consider skyholes — apertures on a surface which permit light to pass through (for example, leaves / foliage).

  • Smaller skyholes should be painted a little darker than the actual sky color if they contain even smaller skyholes that weren’t apparent or visible.
  • Transparent material does not necessarily permit all light to pass through.

• Sunbeams are shafts of light made visible in the presence of a high number of particulates (i.e., high moisture or dusty conditions).

  • The rays of a sunbeam are parallel (except when seen in perspective.
  • They occur when all of the following are present.
    • A high screen (i.e., clouds, foliage or architecture) is punctured by a few openings. The layer must block most of the light to allow a darker backdrop.
    • The air is filled with particulates.
    • The view is towards the sun.
  • The farther away the aperture, the more softened the edges become.
  • Realistically, when sunbeams shine through uneven apertures, the beam has variable density and softness.
  • Shadowbeams occur when a bar of unilluminated vapor is seen edge on.
    • It is only visible when there is a light hazy sky from behind.
    • The illuminated air next to the shadowbeams are slightly lighter in value.

• Dappled Light refers to a type of soft, filtered light that creates a pattern of patches or spots on a surface.

  • The patches are projections of the light source, but filtered through an object (say foliage).
  • If the aperture is high, the dappled light on the ground tends to have larger circles and softer edges.
  • If the aperture is low, the dappled light on the ground will have smaller circles and sharper edges .

• We can use an illuminated foreground so that the background is the one cast in shadow.

• Snow is white and so it picks up the average of all colors around it .

  • Snow exhibits subsurface scattering, especially when it is new or powdery. This is more apparent when the snow is backlit.
  • Light scattered below the surface of snow takes on a blue-green hue.
  • Compacted snow becomes darker (due to dirt).
  • If ice is present, the snow becomes shinier (i.e., with specular reflection)

• Consider the effects of light hitting a water surface..

  • Water causes light to both reflect and refract.
    • Water filters colors towards warmer, darker versions when seen above water.
    • Water absorbs light starting with low-energy light (red). Colors get progressively bluer until it becomes indistinct from the water.
  • Shallow and clear water lets us see the bottom due to refraction.
  • At a shallow angle, water appears as a perfect mirror.
    • Note however that water is not a perfect mirror because only some of the light will be reflected back.
  • Deeper water will appear darker because not much light is reflected back.
    • This also means reflections in deeper water are darker than usual.
    • If the water is dirty and illuminated, darker colors will turn a lighter brown.
    • Note that reflections will be distorted due to waves. In particular horizontal lines are distorted while vertical lines are not.
  • You cannot cast a shadow over deep, clear water.
    • Cast shadows become apparent when the water is dirty. However, the se shadows will be more diffuse than shadows on land because of diffusion.

Links §

• Color Theory

• Color and Lights by Gurney