Light :: radiant energy that is capable of exciting the human retina and creating a visual sensation

Radiant flux :: total power of electromagnetic radiation (measured in watts) emitted/received

Luminous flux :: those wavelengths detectable by the human eyes have this corresponding value; total amount of light emitted by a lamp in all direction

Lumen :: unit of luminous flux; brightness of light; denoted by “lm”

Illuminance :: denoted by “E”; a term given to the quantity of luminous flux falling on a unit area of a surface; measured in lux

Lux :: lumens per square meter; used to determine the number of lights used in a space

Luminance :: denoted by “L”; luminous intensity emitted by a light source per unit area; measured in candela per square meter; reflected light

Reflection :: process by w/c a part of the light falling on a medium leaves that medium from the incident side

Secular :: type of reflection where parallel reflections are made

Spread :: type of reflection where it spreads parallel rays into a cone of reflected rays

Diffuse :: type of reflection that occurs to rough surfaces; reflection is diffused

Compound :: type of reflection that exhibits all 3 reflection components

Refraction :: change in velocity of light that occurs when a ray leaves one material and enters another of greater/lower optical density

Interference :: when two light waves of the same wavelength come together at diff. phases

Diffraction :: phenomena that occurs when light passes by an obstruction producing shadow of the edge

Diffusion :: breaking up and the spread of a beam of light

Absorption :: light passes thru a medium/ meets a dense body

Lamp life :: life expectancy of the lamp

Color temperature :: denoted by “K”; warmness or coolness of white light; expressed in Kelvin; lower K, warmer

5000 K - 6000 K :: light temp commonly used in classrooms, kitchens, offices

2000 K - 2700 K :: light temp commonly used in bedrooms

3000 K :: light temp where mood overrides a need for visual clarity; for low lighting levels

3500 K :: light temp good for showrooms, general merchandising, general work areas; combines warm and cool

4100 K :: cool light temp used for areas of high illumination

5000 K :: crisp and clean color temp; “icy blue”; used for spaces where visual acuity/long range viewing is critical

Color Rendering :: denoted by “Ra”; ability to render colors faithfully is measured using this; has a value from 20 (severe color distortion) to 100 (no distortion)

85 and above Ra :: good color rendering

below 50 Ra :: colors can’t be distinguished

Ambient light :: overall lighting of a room for safety and basic visual recognition

Tasking light :: lighting in a room intended for the performance of a specific task

Focal lighting :: also called accent lighting; used to illuminate features and displays

Decorative lighting :: lighting intended as an ornament to the space

Direct lighting system :: produces 90-100% light downward

Semi-direct lighting system :: produces 10-40% light to ceiling and 60-90% light downward

Indirect lighting system :: produces 90-100% light upward

Semi-indirect lighting system :: produces 60-90% light to ceiling and 10-40% light downward

Direct-indirect lighting system :: 40-60% upward and 40-60% downward; brighter than semi-indirect but soften than direct lighting

Luminaire :: any lighting device that includes a lamp holder and the means of electrification and support for the device

Downlight :: type of stationary light where light is directed predominantly downwards

Double-focus :: high luminous efficiency even though the aperture is small

Washlights :: have asymmetrical lighting distribution; used to highlight; only one side emits light

Directional downlights :: provide accent lighting of specific areas/subject

Air-handling downlights :: represent a dual function solution compromising lighting and air-conditioning

Uplights :: type of stationary light where the light is directed upward; can be used for indirect lighting

Louvered luminaires :: designed for linear light sources; name is derived from the anti-dazzle attachments

Spotlight :: type of movable light used predominantly as an accent light; illuminates a limited area