Combining Identical LEDs: Power Increase or Not?

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Discussion Overview

The discussion revolves around the physical principles governing the combination of two identical LEDs, specifically whether their power outputs can be summed when they are combined. The inquiry includes considerations of spectral profiles and power supply conditions, as well as the implications of light source arrangement.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether combining two identical LEDs, each rated at 300mW, results in a total power output of 600mW, seeking clarification on the underlying physical principles.
  • Another participant suggests that if the power supply conditions remain unchanged, the power outputs of the LEDs can be summed.
  • There is mention of a conflicting perspective that suggests the power outputs should not simply add up, though no clear explanation is provided for this viewpoint.
  • A participant introduces the concept of ETENDUE, explaining that the combination of light sources is limited by this principle, which relates to the area and emission angles of the light sources.
  • It is noted that while the far fields of the LEDs may add up, there is no improvement in concentration possible if the LEDs emit into a wide angle without lenses.
  • Another participant emphasizes that if the LEDs are arranged such that their light does not significantly obstruct each other, there can be an incoherent addition of their outputs, focusing on total power rather than intensity.

Areas of Agreement / Disagreement

Participants express differing views on whether the power outputs of the LEDs can be summed, with some supporting the idea while others raise concerns about the limitations imposed by physical principles like ETENDUE. The discussion remains unresolved regarding the conditions under which the power can be combined.

Contextual Notes

Participants reference various principles and concepts related to light emission and concentration, including ETENDUE and the Lagrange Invariant, without reaching a consensus on their implications for combining LED power outputs.

Learned
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Hello,


I was wondering if anyone know the physical explanation about the following:

What happens if I combine two Identical LEDs with the exact same spectral profile (eg 350-450nm with 400nm center wavelength and peak).

Assuming the total power of each LED in watts is 300mW. Will the combination of the identical LEDs make for 600mW?

If so, why?

If not, Why?


Thanks in advance for your help.
 
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As long as the power supply situation for the LEDs does not change (and therefore both LEDs have the same conditions as the single LED before), you can just add the power.
 


Thanks for the reply. I have heard from people that they are not suppose to add up- although I got no reasonable explanation for why not.

Since you say it should add up. Could you please breifly explain why?
 


Learned said:
Thanks for the reply. I have heard from people that they are not suppose to add up- although I got no reasonable explanation for why not.

Since you say it should add up. Could you please breifly explain why?


Thanks in advance
 


How you add light sources is limited by ETENDUE.

Look it up on Google..Also..Roland Winston..he's the father of this stuff..used to be at
U.of Chicago now at U. of Merced. Also, Juan Minano, Pablo Benitez, Julio Chavez in Spain have done a lot of work in this. There's a couple of books on Amazon.

Basically, area*sin(emission angle half angle) is a constant..in 2d..also called Lagrange Invariant ..this is covered well in books on Non-Imaging Optics.. also look for limits to concentration

so if you have an led without a lens emitting into 180 degrees then you can't concentrate that further. If you put another one next to it the far fields add up , but no concentration improvement possible.

Typical technology for moving flux from one place to another are CEC's (Compound Elliptical Concentrators) or CPC's (Compound Parabolic Concentrators).

I am available for consulting, btw.
 


Learned said:
Since you say it should add up. Could you please breifly explain why?
Assuming that they are not arranged in a way that the light from A hits B in a significant amount or B blocks A it in other ways (and vice versa): You have a simple incoherent addition of two light sources.

The maximal intensity on a (small) surface cannot be increased, but I don't expect that you care about that, as you mentioned the total power.
 

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