In-Depth Notes on Lighting and Vision

Lighting and Vision

  • Concept of Light

    • Light is an electromagnetic energy that plays a crucial role in vision and color perception.

  • Wavelength of Visible Light

    • Visible light falls between 400 nm (violet) to 700 nm (red).
      • Violet: 400 nm
      • Blue: 450 nm
      • Green: 520 nm
      • Yellow: 580 nm
      • Orange: 610 nm
      • Red: 700 nm

Signals and Perception

  • How Vision Occurs
    • Light must reach the eye from a source, reflect off an object, and stimulate receptors in the eye (rods and cones).
    • Rods (120 million): Sensitive to light.
    • Cones (6-7 million): Sensitive to color.
    • Signals are transmitted from the eye to the brain, causing the sensation of vision.

Measuring Light

  • Lumens, Candelas, Illuminance
    • Lumens (lm): Light output (luminous power or flux).
    • Candelas (cd): Intensity of light in a given direction.
    • Foot-candle (fc): Measurement of illuminance on a surface one foot away from a standard candle.
    • 1 foot-candle ≈ 10 lux (SI unit).

Inverse Square Law

  • Intensity of Light
    • The intensity of light decreases as the distance from the source increases.
    • Energy at twice the distance is spread over four times the area, reducing intensity to one-fourth.

Brightness and Luminance

  • Distinction
    • Brightness: Perceived quality of light.
    • Luminance: Measured in candelas per square meter (cd/m²).
    • Lighting professionals distinguish between these two concepts for practical applications.

Visual Characteristics

  • Visual Field

    • Range of vision with sharpness (130°), detail, movement, changes in brightness.

  • Factors Determining Visibility

    • Size, Contrast, Luminance, and Time affect visibility.
    • Larger or closer objects are easier to see.
    • Higher contrast increases visibility.

Color Recognition

  • Light Source vs. Object Color

    • Object color perception depends on the light source's spectral composition.
    • Example:
    • A green light makes leaves appear green while an apple appears black.

  • Spectral Power Distribution (SPD)

    • Represents the color composition of a light source, changes with time, and location.
    • Natural light is variable and complex:
      • Noon Sun: Balanced radiant power
      • Sunrise/Sunset: Different strengths in red/violet wavelengths

Color Temperature and CRI

  • Color Temperature

    • Measured in Kelvin (K), indicates the appearance of light (warm vs. cool).
    • Lower temperatures = warmer light; higher temperatures = cooler light.

  • Correlated Color Temperature (CCT)

    • Incandescent sources have CCT between 2750K and 3200K.
    • Other sources need CCT for comparison.

  • Color Rendering Index (CRI)

    • Compares color rendering properties of different light sources.
    • A CRI of 100 reflects natural color; lower values indicate less natural color rendering.

Summary of Key Points

  • Only see object colors present in the light source.
  • SPD expresses color composition in Kelvin.
  • Color temperature describes apparent white light color using the Kelvin scale.
  • "Warm" and "cool" depend on spectral composition of the light.
  • CRI indicates how natural colors appear under a light source without strict adherence to the Black Body model.