LED Terminology – Kelvin, CRI, and Luminous Flux

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LED Lighting Terminology 
Color Temperature and Color Rendering (Kelvin and CRI): There are two standard measurements for the color characteristics of light: “color rendering index” (CRI), a term used to describe the extent to which an artificial light source is able to render the true color of objects as seen by natural outdoor sunlight which has a CRI of 100, and “color temperature”, which expresses the color appearance of the light itself.

Color Rendering Index (CRI): Incandescent is used as the base reference of 100 CRI. Compact fluorescent lamps are graded at 82-86 CRI, which is considered high quality color rendering. CRI is a more important consideration for retail lighting design than it is for office lighting.  Any CRI rating of 80 or above is considered high and indicates that the source has good color properties. Incandescent lamps and daylight have a CRI of 100, the highest possible CRI. The higher the CRI of the light source, the “truer” it renders color. At M-Lite we strive to manufacture our LED lighting at 80 CRI or better.

Color Temperature (Kelvin): Refers to the way color groups are perceived – the psychological impact of lighting. Color temperature is how cool or warm the light source appears. The color temperature of a light source is a numerical measurement of its color appearance. This temperature is based on the principle that any object will emit light if it is heated to a high enough temperature and that the color of that light will shift in a predictable manner as the temperature is increased. This system is based on the color changes of a black metal as it is heated from a cold black to a white hot state. As the temperature increases, the color would shift gradually from red to orange to yellow to white and finally to a blue white. Color temperature is measured in degrees Kelvin (K). Colors and light sources from the red/orange/yellow side of the spectrum are described as warm (incandescents) and those toward the blue end are referred to as cool (natural daylight).  The sun, for example, rises at approximately 1800 Kelvin and changes from red to orange to yellow and to white as it rises to over 5000 Kelvin at high noon. It then goes back down the scale as it sets.


Luminous Flux – the flow of light measured in lumens. With light bulbs, it provides an estimate of the apparent amount of light the bulb will produce. Depending on the application, much of an incandescent’s light is wasted because it’s emitted in every direction. LEDs on the other hand, put out directional light, sending all of the light exactly where it’s needed. This is why an LED producing 500 lumens might be equivalent to an incandescent producing 900 lumens.

Lumens measure how much light you are getting from a bulb. The more lumens means it’s a brighter light; fewer lumens means it’s a dimmer light.

Lumens produced is just one factor of the performance of a light, and sometimes it is misleading. To understand how to fully evaluate the LED product, we need to look the overall system efficiency, optical control, thermal management of the LEDs.

Another factor that can also be very misleading is the life of an LED lights, the life time is defined by how long will the light last before the fixture reaches 20 percent lumen depreciation.

For example, most of the time an LED Light has a life time of 50,000 hours, it does not mean that after 50,000 hours, the LED lighting product will not work at all. It will still be working, but the Lumens it emitts is factored at 20% less than when it was first used.

For more LED Lighting Facts, visit our website at http://www.m-lites.com

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