Hlp with integrating sphere for RGB LEDs

Hey there everyone!
I’ve been lurking for a while reading up on all the LED experimenting here as I have a fairly specific project in mind, but could use some assistance.

Basically I need a really diffuse light source, that covers as much of the white-light spectrum as possible.

My thought was to use an array of individual RGB LEDs and use an integrating sphere, with the hope that this would give me a white-light output with a really even illumination. I need to illuminate an area about 30mm x 30mm square.
The LEDs need to be driven in a way that does not flicker when viewed with a high-speed camera.

Does this sound like a feasible way to go, or am I misunderstanding how this all works?

I’m also wondering what is the smallest size of sphere I could likely get away with.

Thanks in advance for any help, my apologies if this isn’t the right place to post this.

Welcome to BLF, poia!

An integrating sphere will work well for what you want, I would experiment with a styrofoam ball for that. The size of the ball will depend on the size of your light source: the entrance and exit holes combined have to take up a maximum percentage of the inner surface area (about 5%) to maintain proper integration and therefore the even illuminiation from the exit hole that you want to obtain.

In my signature line below is a link to several integrating spheres that I have build, if you look at number 4, it gives an easy way to build one (this sphere does not have an exit hole, so you will have to add that, and you may have to add a baffle as well to block light from the source going directly through the exit hole).

About the RGB-leds, they will not cover the white spectrum because they will only be narrow peaks at three positions in the spectrum, for spectrum coverage, I would more likely consider a high CRI led.

Thanks djozz, I’ve been reading all of your integrating sphere builds :slight_smile:
They were what inspired me in the first place.
Could you point me towards some high CRI LEDs that might be worth trying?
Can they be driven in a way that makes them constantly on rather than PWM or other ‘flickery’ methods?

I have been toying with the idea of working it out with styrofoam spheres, and then 3D Printing a sphere once I sort it all out, like this one:

https://blog.canary.is/2014/11/19/a-custom-canary-integrating-sphere/
(Scroll down to their blog re using the printed sphere)

Cheers and thanks for the quick response!

A short answer because I need to go to bed:

Look at Nichia 219B V1 92 CRI , it can be bought in 4000K (Illumn.com) and 5000K (Mountain Electronics), or Osam Oslon Square 92 CRI (RS-online, Mouser, Digikey).

Those are all small leds, but in your setup, a high CRI COB-led will work as well and can be bought with very high output.

Flickering only happens when the output needs to be adjusted, so when lower modes are needed. Some drivers make lower modes without PWM (flickering), like the LD2 from BLF-member led4power.