## Frequently Use LED-Related Terminology:

#### Light Output/Lumens

 1) A lumen is a unit of standard measurement used to describe how much light is  contained in a certain area. 2) A lumen is defined as one candela multiplied by one steradian, which can be expressed as: 1(lm) = 1(cd) x 1(sr). A related unit of measurement — although not part of the standard units — is the foot-candle, 3) The higher the number, the more light is emitted.

#### Watts

 1) Measures energy required to light the product. 2) The watt is defined as “the power which in one second gives rise to energy of 1 joule”.  In mechanical terms, a power of 1 watt can, in 1 second, move a mass of 1 kilogram through a distance of 1 meter with such force that the kilogram’s velocity at the end of the meter will be 1 meter per second greater than it was at the beginning. In an electric circuit, 1 watt is a current of 1 ampere at a pressure of 1 volt. 3) The lower the wattage, the less energy used.

#### Lumens per Watt/Efficacy

 1) In lighting design, “efficacy” refers to the amount of light (luminous flux) produced by a light source, usually measured in lumens, as a ratio of the amount of power consumed to produce it, usually measured in watts. 2) This is not to be confused with efficiency which is always a dimensionless ratio of output divided by input which for lighting relates to the watts of visible power as a fraction of the power consumed in watts. 3) The higher the number, the more efficient the product.

#### Color Rendering Index (CRI)

 1) Color rendition is the effect of the lamp’s light spectrum on the color appearance of objects. 2) Scale of 0 to 100, used by manufacturers of fluorescent, metal halide and other nonincandescent lighting equipment to describe the visual effect of the light on colored surfaces. Natural daylight and any light source approximating a blackbody source is assigned a color rendering index (CRI) of 100.

#### Correlated Color Temperature (CCT)

 1) Color Temperature of a light source is defined by its warmth or coolness and is expressed in degrees Kelvin. 2) Color temperatures over 5,000K are called cool colors (blueish white), 3) Lower color temperatures (2,700–3,000 K) are called warm colors (yellowish white through red)