How to Measure an LED's Brightness

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The solid-state lighting industry had a problem. It was the early 2000s and solid-state lighting with light-emitting diodes (LEDs) was making great strides in efficiency, color quality, and brightness — but the customers were not showing up. Because the customers were unfamiliar with the new technology, they needed to trust LED manufacturers’ claims about their performance — but everybody had a different measurement method. Finally the industry adopted measurement standards, and LED fixtures — luminaires — are now being actively sought by a variety of customers. One of the most important measurements is light output, which now has a standard governing its measurement.

Things You'll Need

  • LED luminaire (fixture)
  • Thermally-isolated mount
  • Electrical power supply
  • Temperature stabilizer
  • Integrating sphere
  • Calibrated radiometer
  • Goniometer

Preparatory Steps

  • Put the luminaire on a thermally-isolated mount.

  • Stabilize the temperature at 25 degrees Celsius. Allow the luminaire and mount to come to thermal equilibrium.

  • Connect the luminaire to an electrical supply that will provide the operating power specified by the luminaire manufacturer.

  • Decide on the desired output: total integrated flux (overall brightness) or an intensity distribution (brightness as a function of angle).

Integrated Light Output

Measuring Intensity Distribution

  • Place the luminaire in the goniometer mount.

  • Place the radiometer detector on the measurement arm of the goniometer. The goniometer arm will move the detector around the luminaire, keeping it pointed at the light source at every angle.

  • Turn the luminaire on briefly and record an output measurement.

  • Move the goniometer arm to a new angle, wait for the luminaire to cool down, then turn it on briefly and record another output measurement.

  • Repeat as necessary to measure over the output range of the luminaire. Then add the recorded measurements to determine total lumen output of the luminaire. This method will also provide a measurement of light output for each angle.

Tips & Warnings

  • For more details, get a copy of the Illuminating Engineering Society of North America’s LM-79-08 Standard, "IES Approved Method for the Electrical and Photometric Measurements of Solid-State Lighting Products."

References

  • Photo Credit Kiyoshi Ota/Getty Images News/Getty Images Thinkstock Images/Comstock/Getty Images Miguel Villagran/Getty Images News/Getty Images Medioimages/Photodisc/Photodisc/Getty Images
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