- Light as electromagnetic radiation: Visible light occupies a narrow band between 380 and 700 nanometers. Filmmakers care about wavelength because it determines color; shorter waves appear blue, longer waves appear red. Understanding this spectrum helps predict how gels and filters modify light.
- Inverse square law applied: Light intensity drops proportionally to the square of distance from source. Doubling the distance reduces illumination to one-quarter. This principle explains why a lamp moved from 4 feet to 8 feet away produces significantly dimmer light, requiring compensation with exposure or fixture power.
- Hard vs. soft light sources: Hard light comes from small or distant sources, creating sharp shadows and high contrast. Soft light comes from large or near sources, wrapping around subjects and producing gentle gradations. The ratio of source size to subject distance determines softness.
- Reflection and refraction: Light bounces off surfaces at an angle equal to its incidence. Matte surfaces scatter light diffusely, while glossy surfaces reflect specularly. Refraction occurs when light passes through transparent materials like water or glass, bending the path and changing apparent depth.
- Color temperature basics: Measured in Kelvin, color temperature describes the warmth or coolness of a light source. Tungsten film balanced at 3200K, daylight at 5600K. Lower numbers appear orange, higher numbers appear blue. The human eye adapts automatically, but film and sensors record the actual color cast.
- Light metering for exposure: Incident light meters measure the light falling on a subject, while reflected meters measure light bouncing off it. For consistent skin tones, use an incident meter at the subject position, pointing toward the key light. This gives the F-stop needed for correct exposure.
- Contrast ratio importance: The difference between key light fill side is measured in stops. A 2:1 ratio (one stop difference) yields flat, even lighting typical of comedies. An 8:1 ratio (three stops) produces dramatic shadows common in film noirs. Ratios are controlled by fill light placement and intensity.
- Practical implications of light falloff: Backgrounds in a scene receive less light than foreground subjects due to distance. This natural falloff creates depth, but can be adjusted using flags to cut light or bounce to fill. Light direction also affects how falloff shapes the space.
Principle: Inverse Square Law in Cinematic Depth
Definition: The inverse square law states that illumination decreases with the square of the distance from the source. In film, this principle creates realistic light falloff that separates foreground from background.
Application: For a night interior scene, place the key light 4 feet from the actor's face and let the background fall naturally three stops darker. This 8:1 contrast ratio guides the audience eye to the actor while the background recedes. Avoid using additional fill light on the background if you want to preserve depth.
Harmony: Complementary Color Temperature
Balancing warm and cool sources creates visual tension. Place a 3200K lamp as the key on a subject and let window light (5600K) fill the background. The complementary relationship adds depth and emotional contrast.
- Light wavelengths determine color; shorter = blue, longer = red.
- Inverse square law: intensity decreases with distance squared.
- Hard light = small source, sharp shadows; soft light = large source, gentle gradients.
- Reflection angle equals incidence angle; refraction bends light through transparent media.
- Color temperature measured in Kelvin: tungsten 3200K, daylight 5600K.
- Incident metering from subject position gives accurate exposure for skin tones.
- Contrast ratio controls mood: 2:1 flat, 8:1 dramatic.