light source

• pose

  • position
  • orientation

• support geometry

  • size
  • shape
• magnitude: total source strength
• spatial profile: emission distribution across the source surface
• angular profile: emission distribution by direction
• spectrum: wavelength distribution; approximately temperature + tint when sufficient

lighting system

• source count: number of independently controlled sources
• layering: superposition and spatial arrangement of source contributions

scene

• geometry: surfaces, orientation, distances, occlusion, visibility

• material transport

  • diffuse reflection

  • specular reflection

  • transmission

  • subsurface transport

camera

• viewpoint and projection
• focus / depth response
• exposure integration
• spectral response

• spatial transfer

  • diffraction
  • diffusion
  • bloom
  • halation
  • flare
• recording / tone response

conditional

• temporal profile: flash duration, flicker, synchronization
• polarization: when source, material, or camera is polarization-sensitive

• apparent extent: angular size and shape of the emitting field as seen from the subject
• incidence angle: source direction relative to a surface
• softness: shadow-transition character produced mainly by apparent extent and geometry
• coverage: illuminated region produced by pose, angular profile, and scene geometry
• feathering: placement of the target within a nonuniform angular profile
• spatial falloff: change in illumination across space
• exposure contribution: result of source magnitude, geometry, distribution, spectrum, and receiving surface
• rim / outline: source-scene-camera configuration producing visible edge illumination
• glow: appearance produced by transmission, scattering, broad highlights, diffusion, bloom, halation, flare, or local contrast

• source distance changes apparent extent, exposure, and spatial exposure gradients
• source orientation changes illumination without changing source position
• physical source size != apparent source extent
• source magnitude != received exposure
• same exposure != same lighting
• support geometry != spatial profile
• apparent extent != angular profile
• softness is derived, not a source property
• layering is a relation among sources, not a light property
• scene material can radically change the photographed result without changing the source
• camera spatial transfer can create glow-like structure absent from the scene illumination

inverse-square behavior

• irradiance approaches 1 / distance² for a sufficiently small source in free space
• extended nearby sources require geometric treatment rather than simple point-source approximation

focal length

• controls projection scale and angle of view for a given sensor format
• does not by itself determine perspective; viewpoint does
• longer focal length + greater camera distance can produce narrower framing with compressed apparent depth relations

focus

• correct focus maps a scene depth sharply onto the image plane
• defocus produces blur circles whose size depends on aperture, focus distance, subject distance, focal length, and sensor geometry

aperture

• controls admitted light and contributes to depth of field, diffraction, and blur geometry

viewpoint

• determines perspective and relative geometric projection
• lens choice determines how much of that projected field is recorded

natural light

• sunlight: very distant, small apparent angular source, strongly directional unless modified by atmosphere or environment
• window light: extended source whose apparent extent depends strongly on subject distance and window geometry
• environment can add reflected and transmitted contributions while one source remains dominant
• spectrum varies with time, weather, surroundings, and transmitted/reflected surfaces

studio light

• begin with one motivated dominant source

• control independently:

  • pose
  • apparent extent
  • magnitude
  • angular profile
  • spectrum
• add sources only when an additional independently controlled contribution is required
• avoid accidental conflicts in direction, spectrum, shadow structure, or visual motivation

background

• control independently from the subject when necessary
• gradients arise from source pose, distribution, distance, and background geometry
• black backgrounds emphasize separation, edge structure, and local contrast
• white backgrounds require sufficient illumination and spill control to remain clean
• seamless surfaces and regular edges reduce unintended geometric structure

reference practice

• study photography, film stills, paintings, and CGI by reconstructing:

  • source count
  • source pose
  • apparent extent
  • angular profile
  • relative magnitude
  • spectrum
  • material response
  • camera response