Calculating of the heat dissipation of a LED

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Discussion Overview

The discussion revolves around calculating the heat dissipation of a specific LED model, focusing on its luminous efficacy and the implications for thermal management in a large floodlight application. Participants explore various factors affecting heat generation and efficiency, including quantum efficiency and the relationship between luminous and radiant power.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests that the quantum efficiency of the LED is about 20%, implying that over 80% of the input power will be converted to heat.
  • Another participant questions the adequacy of the luminous efficacy data provided in the datasheet for calculating heat dissipation, proposing a rough estimate of 300lm/W for luminous efficacy.
  • A participant emphasizes the importance of knowing the quantum efficiency to accurately assess heat dissipation, referencing external resources for further understanding.
  • Concerns are raised about the design of the cooling system without prior knowledge of power dissipation requirements, indicating a potential oversight in the design process.
  • Participants discuss the need to convert relative radiant power data into spectral radiant power to facilitate calculations, with one expressing uncertainty about the conversion process.

Areas of Agreement / Disagreement

There is no consensus on the exact values for luminous efficacy or quantum efficiency, and participants express differing views on the adequacy of the provided data for calculations. The discussion remains unresolved regarding the best approach to determine heat dissipation.

Contextual Notes

Participants note limitations in the provided datasheet data and the need for additional information to accurately calculate heat dissipation. There are unresolved assumptions regarding the efficiency and design of the cooling system.

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.
 
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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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