Technical Lighting Terms
Refers to the divergence angle of the light exiting the lamp. The smaller the number, the tighter and brighter the beam.
Used by lighting designers to calculate the foot-candles illuminating a surface (C.P. /distance in feet squared) or Lux illuminating a surface (C.P./distance in meters squared).
Correlated Color Temperature (CCT)
Refers to the apparent color of the light source. 2800K – 3200K considered “warm” ; 4100K-4900K considered “white” and 5000 K + “cool”. Comes from heating a blackbody (think of a piece of coal) up to a certain temperature; as the coal gets hotter and hotter, it changes from orange (i.e., 2300 K) to yellow (3000 K) to white (4700 K) to blue (5000 K) rendering.
Color Rendering Index (CRI)
Measure of how well a light source replicates a given lighting condition; 100 being perfect, 90 fair, 80 poor.
Combination of direct sunlight and skylight. Best light for optimal color rendering.
Measurement of light output in candelas per square foot. 100-foot candles is generally considered enough light to perform most tasks.
Infared Radiation (I.R)
Associated with sunburns and heat. Lower energy, long wavelength energy situated at the red end of the visible light spectrum.
Measurement of a quantity of light as perceived by the human eye. As a light source’s color temperature increases, less light is required to achieve comparable brightness and visual acuity.
Measurement of light output in candelas per square meter. 10 lux is generally Considered enough light to perform most tasks.
Ultraviolet Radiation (U.V.)
Associated with suntans and fading of pigments and dyes. High-energy short wavelengths before the blue end of the visible light spectrum.