Physics Chapter on Light and Its Behavior

Study Notes

Illuminance is the amount of light striking a surface.
Luminance is the amount of light leaving an object; it's how bright the object appears.
Reflectance is the ratio of reflected light to the light striking the surface.
- Specular reflectance occurs on polished surfaces, maintaining the reflected image.
- Diffuse reflectance occurs on rough surfaces, scattering the reflected light.
Transmittance is the ratio of transmitted light to the light striking the surface.
- Transparent bodies allow light to pass through without distorting the image.
- Translucent bodies allow light to pass through but obscure the image as it's scattered.
Absorptance is the ratio of absorbed light to the light striking the surface.
- Opaque bodies reflect and absorb light, but do not transmit it.

Color perception is our ability to distinguish and interpret different wavelengths of visible light.
The perceived color of an object is determined by the dominant wavelength it reflects.
Surfaces that reflect all wavelengths appear bright in natural light.
Surfaces that absorb all wavelengths appear black in natural light.
Visual acuity refers to our ability to distinguish fine details and is crucial for tasks requiring precision.

Luminous Flux: Measures the perceived power of light, expressed in lumens (lm).
Luminous Intensity: Measures the power emitted by a light source in a particular direction, expressed in candelas (cd).
Luminous Efficacy: The ratio of a lamp's light output to its consumed electrical energy, used to determine its efficiency.
Color Rendering Index (CRI): Numerically compares the color distribution of a light source to a reference lamp to determine how well it renders colors.

Lamp Type	Rated Power (Watts)	Efficacy (Lumens per Watt)	Minimum CRI
Incandescent	10 - 100	10 - 100	100
CFL	3 - 125	41 - 65	80
Linear
Halophosphate	10 - 40	55 - 70	70
Triphosphor	14 - 65	60 - 83	80
Mercury	50 - 2000	40 - 63	20
Metal Halide	Up to 1000	75 - 95	65
LPS	20 - 2000	100 - 180	0
HPS	20 - 250	80 - 130	21

Expressed in Kelvin (K)
Warm lighting emits mostly red and yellow wavelengths (below 3200K).
Cool lighting emits mostly blue and white wavelengths (above 5000K).
Daylighting has a temperature between warm and cool, with the lower end warmer (around 4100K) and the upper end cooler (around 6500K).

### Lamp Types

Average Efficacy: 12 lumens per Watt for a 40 watt T-12 fluorescent lamp.
Daylight: 51 lumens per watt. Used where color matching is crucial. Equivalent to north sky light but not commonly used due to its high proportion of blue.
Cool White: 58 Lumens per watt. Combines high efficacy with...