What are"cold" and"hot" lumens?
The LED street light project requested:
?Minimum efficiency of LED lamps More than 149-169 lm/W from the lamp (hot lumen)
I have tried some of your IES files you have sent me and it would be workable ... all the lumens output are HOT LUMEN? This is important to know ... because 20W is OK but can not be less than the Dialux. In this case, it would not be HOT lumens I would take 30W...
These terms do not have any photometric or engineering meaning. However, "cold lumens" is the light output of the LED chip alone when it is first switched on. "Hot lumens", refers to the light output of the LED when it is fully warmed up in the luminaire. The hot lumen value may be 30% - 50% lower than the cold lumen value.
I am surprised the hot lumen value may be 30%-50% lower than the cold lumen value. The difference is so big! Normally, the IES files are hot lumens or cold lumens? When it is tested after production, it should be cold lumens.
The following information is from NexusLED Green Technology Sdn. Bhd.
What is “Hot Lumen and Cold Lumen” Light output?
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The term “Hot Lumen and Cold Lumen” is basically used in LEDs light output. Lumens are the measure of the light output of any lighting source.
In case of LEDs, Cold Lumens are the light output measured at standard test conditions that is under 25 Degree C junction temperature of LEDs, whereas Hot lumens are the typical lumens delivered by the LED at junction temperature at about 80-85 degree C at a normal working temperature of the surroundings.
Lots of people got confused that they have the misconception that if the LED manufacturer says 140Lumens/Watt at 25 Degree C, they are getting an effective 140Lumens/Watt. This is totally wrong, when the junction temperature of LED increases the Lumens decrease as there is Junction temperature and Lumen are inversely proportional to each other. Every reputed LED manufacturer like Philips, Osram, Cree, and Nichia.. provides all such details in their LED datasheet.
Now I better understand why the heatsink performance is so important on LED fixtures. Junction temperature is a function of:
How are LEDs affected by heat?
In general, the cooler the environment, the higher an LED's light output will be. Higher temperatures generally reduce light output. In warmer environments and at higher currents, the temperature of the semiconducting element increases. The light output of an LED for a constant current varies as a function of its junction temperature. The figure above shows the light output of several LEDs as a function of junction temperature.