Color Rendering Index (CRI)

The CRI of a lamp, is a number from 20 to 100; that describes how well the lamp’s light emission affects the appearance and vibrancy of an object’s color.  It is determined by comparing the lamp with a reference source of the same Kelvin temperature.

Kelvin (K)

Kelvin is the basic unit of measurement for temperature. Zero (0) Kelvin = -273.15° centigrade.  The Kelvin temperature rating of light, is based on the color most highly emitted.  It does not express the range of a lamp’s light spectrum or the strength of it’s illumination (radiant power).

Correlated Color Temperature (CCT)

The CCT number is a measurement of the actual color appearance of light. It is expressed in Kelvins. Low CCT numbers define “warm” lighting, like the yellow and red hues of candlelight at 1500K. High CCT numbers define “cool” lighting, like a clear blue sky at 12000K. Actual light that we see measures from a low of 2000K to a high of 7500K.

Footcandle (fc) and LUX (lx)

FC and LX are unit's of luminance (light on a surface).  1fc=lm/ft2; 1lx=lm/m2; 1fc=0.0929lx; 50 footcandle is generally considered sufficient for most tasks.

Lumen (lm)

A lumen is the standard unit of luminous flux (the time rate of flow of radiant energy). This is a measurement at the light source (the lamp), not necessarily at the surface being lit.

Nanometer (nm)

A nanometer is the extremely small unit used to measure lengths of light waves. A single nm equals one billionth of a meter.

Watt

A watt is a unit of power equal to work done at the rate of one joule (approximately 0.738 foot pounds) per second. Wattage is actually a measurement of energy, not of light.