What percentage of heat is generated from LED lighting?

[Howlin]

Hi all,

If in a room, a lighting design was carried out and the room will contain 4 no, LED luminaries with a total wattage of 80.

My query relates to what would a reasonable figure or percentage be to use as heat gain from the light. Of the 80 watts, how much of it would go into heat?

I am unable to find it in either a CIBSE guide or an Ashrea guide.

Your help would be gratefully welcomed.

 

[Baluncore]

An incandescent filament is less than 5% efficient at producing light.
An LED is about 10 times better than an incandescent filament.
An LED is therefore less than 50% efficiency.

Most of the 80 watt supplied will appear as heat. Heat rises.
Most of that heat will appear in the ceiling, roof space or in the floor of the room above.

The light radiated by the LED will also become heat if it is absorbed in the illuminated room.

 

[Howlin]

Hi Baluncore,

Thank you for the reply.

Do you know of any studies or publications that indicate an appropriate percentage heat gain percentage from LED lighting?

I have found some but they don't mention what percentage of the say 80 watts would be lighting and what % would be heat gain.

 

[Baluncore]

In the end, it will all become heat.
Assume 30% immediately becomes light, and 70% heat in the luminaire.
Unless the light radiates through a window, it too will quickly become heat, making all 80 watt heat.
The answer will probably depend on why you ask the question.

 

[russ_watters]

Of the 80 watts, how much of it would go into heat?

All of it. The type of light isn't relevant.

 

[russ_watters]

In the end, it will all become heat...

The answer will probably depend on why you ask the question.

There's one common scenario where how much of the heat gets into the room or HVAC system can depend on configuration: above ceiling fixtures(protruding). If the heat from the driver goes into the ceiling space instead of the room, it may not all find it's way back into the room or HVAC system.

That should be discussed in the ASHRAE handbook somewhere an/or be a check box in load calc software, but I don't have a specific reference off the top of my head. "All of it" is the safe assumption.

[edit] oops, you pretty much covered that in the other post.