Time of Day

As a human living on the planet Earth, we have learned that various lighting scenarios are linked to certain times of day. In the simplest way, we can differentiate between daytime and nighttime. If we examine additional clues, we can identify a sunset, sunrise, or mid-day. Sunrise and sunset generally produce more saturated colors that tend toward reds and yellows (Figure 1.1). Sun light from a sunset or sunrise arrives at a lower angle as the sun nears the horizon. (The only difference between a sunrise and sunset is the sun’s relative direction of travel—whereby it arrives or departs from view.) In contrast, sun light at mid-day arrives from a high angle. Depending on the season and the location, the mid-day sun approaches at a perpendicular angle to the ground. On a clear day, sunlight at mid-day appears more blue.

Time of day is not limited to natural light sources. If the sole source of light is an artificial source, such as a lamp, one can assume that it is night. Alternately, one can assume that the location is in a closed space that prevents sun light from entering. Examples include a cavern, a theater auditorium, or a room with shuttered windows.

Light Sources and Location

Through life experiences, humans learn that various lighting qualities are associated with particular light sources. In addition, clues on the location can be taken from the light information. Table 1.1 includes a few common examples.

Note that moon light is another major source of naturally-occurring light. However, moon light is sun light reflected off the moon’s surface. Hence, moon light can be treated as a weaker source of sun light.

Mood

Mood is a temporary feeling. Moods are often triggered by particular lighting scenarios. For example, people generally associate happiness with bright sunlight. In an opposite way, people associate unhappiness, dreariness, or gloominess with the dim lighting of an overcast sky. The soft, warm illumination of fire light or candle light often enhances beauty or attractiveness and is thus associated with romance. Along the same lines, fashion photography often employs various forms of stylistic lighting to maximize beauty while minimizing the natural defects that all humans carry (such as wrinkles, scars, and so on). When I use the term stylistic, I am referring to light scenarios that generally do not occur in the real world without manipulation.

You can alter mood with artificial light sources. This is a common trick of cinematographers and videographers. For example, to portray a moon lit scene in film, a blue light or blue color balance is sometimes used. To increase tension within a horror film, highly saturated and stylistic lights, such as those with red or green color, may be employed. These lights are sometimes placed at unusual locations so that the lights create exaggerated highlights and shadows (Figure 1.3).

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Light Shadowing

A shadow is a dark area created when an object comes between a light source and a surface. In this scenario, light is blocked from the surface. Even though a shadow results from the lack of light, it also communicates important information. For example, a shadow indicates the direction of a light source. If a shadow extends a great length away from the object, then the light source arrives at a low angle (parallel to the surface receiving the shadow). Hence, sunset light creates “long” shadows. If the shadow tightly surrounds the object, the light source is above the object. Hence, noon-time sun creates “short” shadows (top of Figure 1.4).

The quality of the shadow can also give clues to the nature of the light source. For example, if the shadow edge is sharp and clearly defined, the light source is generating parallel rays of light. This form of light is most often created by the sun on a clear day. If the shadow is clearly defined near the shadowed object but becomes soft over distance, the light source is most likely close by and is man-made (bottom of Figure 1.4). An incandescent light bulb creates this effect.

Wavelength, Color, and Temperature

Electromagnetic radiation travels through the vacuum of space in a straight line at a fixed speed (3×10⁸ meters/second). However, the fluctuating energy state of the associated photons can be described with a wave-like pattern with peaks and valleys. Different forms of radiation possesses different wavelengths. A wavelength is the distance of successive peaks of a wave. With electromagnetic radiation, wavelength is measured in nanometers. A nanometer is one billionth of a meter and is written as nm. Different wavelengths are perceived as different colors by the human brain. For example, “long” wavelengths within the visible spectrum are perceived as magenta or red. “Short” wavelengths within the visible spectrum are perceived as blue or violet. Wavelengths within the visible spectrum fall between 400 and 700 nm (Figure 1.5).

A light source, such as the sun or a light bulb, releases electromagnetic radiation as its material is heated. The sun undergoes nuclear fusion due to the extreme pressures at the sun’s core. A light bulb filament is heated when electricity is passed through the filament wire, which possesses high electrical resistance. Hence, heat (which is produced by the vibration of electrons attached to the atoms of the material) is converted to visible light. As such, there is a direct correlation between temperature and the color of visible light (Figure 1.5). For example, the temperature of an incandescent light bulb filament falls between 2800 and 3700 kelvin. A kelvin, written as K, is a unit of measure for temperature based on an absolute scale, where 0 kelvin is the point at which all atomic vibration has ceased (and no heat is generated). The kelvin scale employs an ideal black body radiator, which is a theoretical material that absorbs all incident electromagnetic radiation. As such, the term color temperature refers to a temperature of a black body in kelvin. This scale is used to correlate the visible color of lights. Lower K temperatures appear orange or yellow. Higher K temperatures appear blue. For example, the sun’s light, when affected by the Earth’s atmosphere, may range from 4800 K (direct sunlight) to 7000 K (cloudy sky) to 9500 K (clear blue sky). Sun light from a sunrise or sunset is closer to 3200 K. Hence, a sunrise or sunset often produces an orange light, much like an incandescent light bulb with a similar color temperature. Some light bulbs, whether they are incandescent, fluorescent, or LED, are labeled “daylight,” indicating their 5000 K to 6500 K color temperature that’s equivalent to sun light on a bright day.

Reflection, Transmission, and Absorption

Light is described as having a continuous range of wavelengths. However, when light with a specific wavelength reaches a material surface, one of three things happens:

If the frequency of the light matches the natural vibrational frequency of the atom’s electrons, the light is absorbed and the light energy is converted into vibrational motion, which in turn is perceived as heat. If the frequency of the light does not match the natural vibrational frequency of the atom’s electrons, the light is re-emitted through reflection or transmission. Frequency refers to the number of occurrences within a particular time frame. Hence, a light wavelength will have a particular number of peaks and valleys over a time frame. The oscillation of an electron’s vibration can also be defined as a wave.

Materials do not contain color. Color is perceived because a material reflects or transmits specific wavelengths. For example, if a ball appears red, it’s because the material of the ball absorbs all the visible wavelengths except for red; the red wavelength thereby is emitted toward the viewer. By the same token, the reflected light may not maintain the original wavelength. Hence, blue sunlight may no longer appear blue when reflected off of a red surface. That said, light color tends to color bleed, whereby the color of one surface affects the color of a second surface. For example, the light reflected off a red backdrop may influence the color of white statues (Figure 1.7). In this case, the statues reflect a pinkish color toward the viewer. Hence, the red of the backdrop and the white of the statues is mixed. If a material appears pure white, it reflects most of the visible wavelengths. If a material appears pure black, it absorbs most of the visible wavelengths (hence, black surfaces become hot more quickly under a light source).

Reflected light does not travel back on its original trajectory. Instead, the light follows an angle of reflection, which is equal to the angle of incidence but is mirrored on the opposite side of the surface normal. A surface normal is a line drawn perpendicular to the surface (see the center of Figure 1.6). When describing reflections and transmissions, light arriving at a specific angle is often referred to as a light ray. Light rays are also used to discuss ray tracing systems within 3D programs. The angle of incidence is the angle between the arriving light ray and the surface normal. As such, the incident light ray, the surface normal, and the reflection ray all lie in the same plane. Note that a reflection only occurs at a material interface (where two materials meet). For example, an interface may exist between the air and a hard surface, such as a piece of stone or metal. Light rays may be described as vectors. A vector mathematically defines direction and magnitude in 3D space.

When discussing 3D lighting, transmission is often referred to as refraction. This is due to the refraction of light. When light is transmitted through a surface, its speed is affected. The change in light speed causes the apparent light direction to change. Hence, objects refracted by a surface appear bent, warped, or broken. You can see this when you place a straw in a glass of water or if you peer through water drops (Figure 1.8). Due to their atomic makeups, different materials produce different degrees of refraction. The refractiveness is measured as a refractive index, which is a mathematical formula that relates the speed of light in a vacuum to the speed of light through a particular material.

Story Communication

This category communicates common information humans have come to expect from light. As discussed earlier in this chapter, this includes the sources of light, general location, and the time of day. Longer time periods can also be inferred with lighting. For example, bright, yellowish sunlight may be associated with warm summer, while dim, blue or gray light may be associated with a cold winter (Figure 1.9).

When the art is sequential and tells a story over time, such as a stage play, a motion picture, or an animation, changes in lighting can communicate changes in time. For example, if the lighting switches from what looks like afternoon to what looks like night, you can assume that the story has jumped to a point a few hours later.

Aside from time information, lighting may be used to communicate specific story details. For example, lighting can create a focal point that reveals important element of the plot or stresses an important component of the scene (Figure 1.10 and 1.11). A focal point is an area of the composition that naturally draws the viewer’s attention.

Mood can also be established to communicate the mental state of the characters or to instigate a sense of negative foreboding or positive anticipation in the viewer. For example, in Figure 1.12, the extensive use of blue color within the clothing, background, and shadow areas make the subject appear depressed; the blue color, even if it was a stylistic invention, infers the presence of a blue light source. In Figure 1.13, red Christmas lights allude to the violence that will occur as part of a holiday horror plot—this serves as foreshadowing for the audience.

Visual Clarity

Visual clarity is quality imparted to a scene, shot, or frame that makes the subject easily identifiable and understandable. The clarity is in reference to the visual quality of the scene, shot, or frame and not necessarily the story. For example, you can light actors or characters so they can be clearly seen against a background. A common example of this is the use of a rim light. A rim light creates a thin line of light on the character edge (Figure 1.14).

The use of a focal point can also be employed for visual clarity. For example, in Figure 1.15, a potentially cluttered scene is simplified by allowing parts of the set to remain unlit. As such, there are several focal points: the reflection of the man on the left, the intercom speaker on the right, and the two men in the background.

Along those lines, lighting can help establish a visual hierarchy, which is the arrangement of elements within a composition or setting that establishes importance. For example, if part of a frame is left dark and poorly lit, its importance to the viewer is diminished. When lighting performers on a stage, a bright spot light focused on one performer causes the audience to watch that performer. Other performers might be present—however, if they are lit with weaker lights, they will receive less attention.

Replication of Real World Locations

A common task within the arts is the replication of a real location. With a painting, there may be a desire to capture the lighting present at a real location during a specific time of day. With motion picture or television work, it may be necessary to alter the time of day or apparent time period at a real location or recreate a particular location on a sound stage (Figure 1.16). With 3D animation created for a visual effects job, it is often necessary to match the lighting that’s contained within pre-existing film or video footage; for example, a 3D car must take on the same lighting contained within a live-action shot in order to integrate the 3D car believably.

Aesthetic Stylization

As discussed in the Introduction, an aesthetic is a set of principles that guide the lighting choices. An aesthetic may be rooted in reality, where the lighting attempts to recreate common lighting scenarios in the real world. On the other hand, the lighting may attempt stylization, where there is no direct attempt to mimic the real world. Examples of stylistic lighting include abstract stage and concert lighting (Figure 1.17). We’ll take a closer look at stylization in Chapter 7.