Calculating of the heat dissipation of a LED

AI Thread Summary
The discussion revolves around calculating the heat dissipation of a specific LED model, which has a luminous efficacy of 157 lm/W at 700 mA. Participants emphasize that approximately 80% of the input power will convert to heat, necessitating effective cooling to maintain efficiency and longevity. The user is tasked with assessing whether 400 of these LEDs in a floodlight will overheat, noting that the datasheet may lack sufficient data for accurate calculations. There is a consensus that understanding the LED's quantum efficiency is crucial for determining the actual heat dissipation. The conversation highlights the importance of designing cooling solutions based on power dissipation requirements.
NJZFW
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Hello Forum,

I write you with the challenge of calculation the heat dissipation of a LED.

The LED in question is http://www.seoulsemicon.com/en/product/spec/SZ5-M3-W0-00/22
a download of the datasheet is possible.

The LED binning is 290lm (W4, 5000K) at 700mA, the efficacy is 157lm/Watt,electrical

I think I need to convert der chart "relative radiant Power over wavelength [%]" in "spectral radiant Power (W/nm) [%]".
But Iam not sure how!

Thanks in advance!
 
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Welcome to PF.
At best, you can expect about 20% quantum efficiency from an LED.
The heat will therefore be greater than 80% of total power input.
You must run the LED cool for high efficiency, and for long life.
That suggests you should design for 100% heat generation.
Vf = 2.85 V. If = 700 mA.
Maximum heat generation is 2.85 * 0.7 = 2.0 watt.
At best, that might be a 20% overestimate.
 
NJZFW said:
I write you with the challenge of calculation the heat dissipation of a LED.

The LED in question is http://www.seoulsemicon.com/en/product/spec/SZ5-M3-W0-00/22
a download of the datasheet is possible.

So using the initial numbers from @Baluncore can you say what type if heat sink and enclosure you have in mind for this? Will there be multiple of those LEDs in the same fixture on the same heat sink?
 
Hi you two and thanks for the replies.

The cooling is already set, my task is to calculate if there will be overheating.
Roughly 400 of those LED's are used in a big floodlight.

What I need is basically the luminous efficacy of the LED (luminous flow/radiant flow). At this point I am quite sure the provided data in the datasheet is not enough to calculate that number.

My rough estimate of those LED is a luminous efficacy of 300lm/W which results in a energetic efficacy of roughly 40%. So about 60% of the total elctric power, dissipates a heat. Therefore it would be not expedient to use the assumption of 100%.

Once I figure it out I will write you share my information-
 
NJZFW said:
The cooling is already set, my task is to calculate if there will be overheating.
That sounds kind of backwards, no? Who "designed" the enclosure and cooling without knowing the power dissipation requirements?
 

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