# Is it possible to combine LEDs of the same wavelength range to get more illumination?

1. May 11, 2012

### Learned

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?

2. May 11, 2012

### Staff: Mentor

Re: Is it possible to combine LEDs of the same wavelength range to get more illuminat

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.

3. May 11, 2012

### Learned

Re: Is it possible to combine LEDs of the same wavelength range to get more illuminat

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?

4. May 11, 2012

### Learned

Re: Is it possible to combine LEDs of the same wavelength range to get more illuminat

5. May 11, 2012

### imagidelic

Re: Is it possible to combine LEDs of the same wavelength range to get more illuminat

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.

6. May 12, 2012

### Staff: Mentor

Re: Is it possible to combine LEDs of the same wavelength range to get more illuminat

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.