What is Relative Photometry?

What is relative photometry?

Total Lumen output of a bare lamp is measured in relative photometry   for more clarity; the total luminous flux of the lamp is measured separately without the Fixture. In IES LM-80- 08, IES LM 82-12, the relative photometry is used. The purpose is to find light output, Efficacy, color over temperature for light engines.

Relative photometry can measures:

• Total luminous flux of the bare lamp
• Luminous intensity distribution
• Scale the luminous intensity values by the ratio of the measured lamp lumens to the rated lamp lumens.

Some important features regarding relative photometry:

1. Relative photometry is performed for luminaries with conventional sources.
2. Luminaries test is referenced to the luminous Flux measured for bare lamp.
3. The result produced is in the units of candela per rated lumens( cd/rated lm)
4. It can also measure the efficiency of luminary.
5. Normalize ballast factor, Lamp age.
6. Specific lamp performance doesn’t matter

Relative photometry is not used in SSL with integrated lamps due to many reasons:

• The LED‘s are difficult to remove from the Luminaries.
• A large number of LED devices will not work properly without heat sinks provided with luminaries.
• The thermal environment that the LED devices undergo within the luminary is often radically different from the thermal environment it will practice in its “bare lamp” configuration.

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