Glossary of Terms

CU (Coefficient of Utilization )	The ratio of lumens from a luminaire (fixture) received on the workplane to the lumens emitted by the luminaire’s lamps alone.
General Area	The percentage of the area of an individual space type that is considered to be general and illuminated with general lighting.
HFC Horizontal Footcandle	Quantity of light (measured in footcandles) on a horizontal surface.
Luminous Efficacy (LE)	The total lumens emitted by a light source divided by the total lamp power input, expressed as lumens per watt.
LDD (Luminaire Dirt Depreciation)	An adjustment factor that accounts for the fractional loss of task illuminance due to luminaire dirt accumulation.
LLD (Lamp Lumen Depreciation)	An adjustment factor that accounts for the fractional loss of lamp lumens at rated operating conditions that progressively occurs during lamp operation.
Lens	A glass or plastic element used in luminaires (fixtures) to change the direction and control the distribution of light rays.
Light Distribution	The way in which light is emitted from a luminaire (fixture); often classified as direct, semi-direct, diffuse, semi-indirect or indirect.
Light Source	The lighting technology that is applicable to the specific luminaire. Typically: compact fluorescent - CF, fluorescent - FL, incandescent - INC, metal halide - MH, miniature reflector incandescent - MR, parabolic incandescent - PAR, tungsten halogen - TH.
LLF (Light Loss Factor)	The fractional remainder of task illuminance due to all combined lumen depreciations including LDD, LLD, and RSDD.
LPD (Lighting Power Density)	A measure of electrical power used to provide lighting to a space - expressed in watts per square foot (or watts per square meter).
RCR (Room Cavity Ratio)	A number relating the dimensions of an enclosed space ( length, width, height) that effects the overall coefficient of Utilization of a luminaire within that specific space. The actual values used in the calculations were: 1 for RCR A, 5 for RCR B, and 7 for RCR C
Recommended Light Level	The horizontal light level (expressed in footcandles) that is considered appropriate for the space or area. These values are generally taken from published IESNA data where applicable.
Reflectance	The ratio of light reflected from a surface to the light falling on the surface.
RSDD (Room Surface Dirt Depreciation)	An adjustment factor that accounts for the fractional loss of task illumination due to dirt on room surfaces.
Size	The size of a lens covering a luminaire opening – typically applied to downlights.
Source	A reference to the source of the building space-by-space description and square footage data (typically sets of building plans) from which building space square footage takeoffs are completed.
Task Area	The percentage of the area of an individual space type that is considered to be for specific tasks and illuminated with task lighting.
TEF (Total Efficiency Factor )	A total efficiency factor used in calculating space type LPDs that includes initial Lamp Efficacy, Light Loss Factor (LLF), and Coefficient of Utilization (CU) and is expressed in lumens per watt.
Weighted Average Footcandles	The footcandle level considered to be typical over an entire space that accounts for both general and task footcandle levels and the space to which each is applied.
Weighted Average LPD	The allowable LPD value for a building type (i.e. office, fire station, library). This value is an average of the whole building LPD values for multiple buildings of this type. This value can be "weighted" in favor of one or more of these individual buildings if that building exhibits unique characteristics within its general type and there is data to support its actual share of new construction. Currently all buildings within a building type are given equal weight.