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LED Basics

LEDs are a two conductor Light Emitting Diode (LED) that releases energy in the form of Photons when suitable voltage is applied. Most LEDs produce a blue light and the phosphor coating on the LED are excited by the photons producing the balance of the visible spectrum to produce white light in various degrees of color temperatures from warm to cool (2300K to 4100K beings most common).

Color Temperature is measured in absolute temperature in degrees Kelvin as compared to a theoretical Black-Body Radiator (BBR) that quantifies the tonality (warmth or coolness) of the light. It is extremely important that you determine what your preferences are for your space and color scheme prior to purchasing fixtures or lamps to assure the results are what you desire.

Color Rendering Index (CRI) is a rating that measures the sources ability to render colors as compared to a BBR at like chromaticity, meaning they are same color temperature, so results of these tests can only be used to compare to like color temperature sources. Results start at 100 and go down (perfect match to BBR = 100.)

  • Results of CRI ratings over 70 are minimum standard (70+ CRI)
  • Results of CRI ratings over 80 are good (80+ CRI)
  • Results of CRI ratings over 90 are very good (90+ CRI)

The LED rapid expansion in lighting applications is due to efficiency now hitting upwards of 100 Lumens Per Watt (LPW) as compared to incandescent that produce from 10-18 LPW depending on lamp. Add to this average rated lamp life from 25,000 to 50,000 hours and you have winning combination.

Stay tuned for the next LED Basics post covering McAdams Ellipse and the LED Binning Process.


Written By: Al Thomas, Director of Lighting Design Services for North Coast Lighting. Al has over 41 years of experience in the industry  in lighting design and as an educator. He has served on the American Lighting Association’s  Consultant Committee for the past 20 years and was the driving force on establishing the latest testing for the Certified Lighting Consultant exam and updates to the Lighting Specialist Training Manuals.