By Richard Gaughan
Updated Mar 24, 2022

In the early 2000s, solid‑state lighting began to outpace traditional lamps in efficiency, color quality, and brightness. Yet customers were hesitant, uncertain whether manufacturers’ claims held up in practice. The industry resolved this by adopting unified measurement standards, ensuring that LED luminaires are now evaluated with consistent, reliable metrics. Light output – the most critical performance indicator – is now governed by a strict, internationally recognized standard.

Preparatory Steps

Step 1

Place the luminaire on a thermally‑isolated mount.

Step 2

Stabilize the temperature at 25 °C, allowing the luminaire and mount to reach thermal equilibrium.

Step 3

Connect the luminaire to an electrical supply that delivers the operating power specified by the manufacturer.

Step 4

Decide whether you will measure total integrated flux (overall brightness) or the intensity distribution (brightness as a function of angle).

Integrated Light Output

Step 1

Place the luminaire mount inside the integrating sphere. For directional lamps, mount it at the side of the sphere; for others, center it.

Step 2

Position the radiometer detector at a side port of the sphere.

Step 3

Turn on the luminaire briefly and record the light output.

Step 4

Multiply the measured output by the calibration factor specific to your integrating sphere – this yields the total lumen output. Calibration factors are typically stored in the radiometer during its overall calibration.

Measuring Intensity Distribution

Step 1

Mount the luminaire in a goniometer fixture.

Step 2

Place the radiometer detector on the goniometer’s measurement arm, which keeps the detector pointed at the source as it moves.

Step 3

Turn the luminaire on briefly and record an output measurement.

Step 4

Rotate the goniometer arm to a new angle, allow the luminaire to cool, then repeat the measurement.

Step 5

Continue sampling across the desired angular range. Summing all recorded values gives the total lumen output, while each individual reading maps the intensity distribution.

Things Needed

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

TL;DR (Too Long; Didn’t Read)

For full details, consult 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.”