Mixing Rebels for high CRI

[Th232]

Hi guys, one of my current projects is making a high CRI floodlight, my overall aim is to get a good high CRI source and hopefully with good CCT.

I've got space for 42 Rebels (use of Rebels here is non-negotiable), and I'm wondering what combination of white and which colours I should be going for. I'm running 2 strings of 21, so I'd prefer to have an even number of each type.

Plan for the white Rebels are the neutral white variant of the new Rebel ESs here.

I was eyeballing the cool white variant, but Future Electronics is out of them, and searching Luxeon Star doesn't come up with any results so that's a moot point at this stage.

I've dug up an image from Don/McGizmo where he measured the spectrum of the noon day sun in Maui and compared it with his high CRI 083s. I've then superimposed the distribution from the neutral white Rebels on it to get this:

From this and other research I've so far come up with this:
14 neutral white (LXML-PWN2) for a total of ~2800 lm
3 red (LXML-PD01-0040) for a total of ~255 lm
2 amber (LXM2-PL01-0000) for a total of ~265 lm
2 cyan (LXML-PE01-0070) for a total of ~260 lm

Side note: total efficiency by my count is ~77.5 lm/W

I'm trying to get as close to that noon day sun as possible, is there anything else I can do better? In particular I don't like the looks of that 480 nm trough, but I'm not sure what else I can do other than swapping a couple of the whites to cyan.

General comments on a better mix of colours would also be appreciated. I've got another train of thought saying that I should dump the reds and just focus on the cyans and ambers. Something like 15 whites, 3 ambers and 3 cyans perhaps? Also tossing up using the blue Rebels, but with the highest binned ones being 58 lm @ 700 mA I'm wondering how many I'd need to make a reasonable difference.

 

[HarryN]

Hi, Perhaps consider to start with the high CRI 4000 K rebels, and fill in from there vs with a low CRI and filling in. LXM3-PW51

The 480 trough is a pain, because there just isn't an easy way to fill it in - no available Rebel, or much of anything else out there.

With that many led spaces, I guess you could also consider using monochromatic versions and building it up that way. This works well, but often requires control of the individual LEDs for blending.

 

[saabluster]

First off I don't consider myself an absolute expert in color mixing although I have done a bit of experimentation with it. I really never saw much benefit to adding amber to the mix myself unless you are just trying to lower the CCT. I would probably just use 4 reds and two cyan. Since I am familiar with your design I would suggest mounting the cyan dead center with the two reds immediately flanking. This will reduce the colored shadows.

 

[Linger]

A huge advantage of Rebel's is they are binned so well. So there's a good mix of 2700k, 3500k, 4000k, etc.
I'd suggest having a look through
http://www.luxeonstar.com/Luxeon-Rebel-LEDs-s/1.htm
again. It just seems like you've made such a great choice going to Rebel's that it'd be a shame to close the door to most of their product line and pick 14 of the same.
The most I've mixed is 4 bins in one light but the results are great. You'll have excellent success with so many emitters.

 

[saabluster]

A huge advantage of Rebel's is they are binned so well. So there's a good mix of 2700k, 3500k, 4000k, etc.
I'd suggest having a look through
http://www.luxeonstar.com/Luxeon-Rebel-LEDs-s/1.htm
again. It just seems like you've made such a great choice going to Rebel's that it'd be a shame to close the door to most of their product line and pick 14 of the same.
The most I've mixed is 4 bins in one light but the results are great. You'll have excellent success with so many emitters.

Good advice. I have noticed the same myself. Mixing cool with warm seems better to my eyes than just neutral even if the CCT is exactly the same.

 

[MichaelW]

Seen this one?
http://www.candlepowerforums.com/vb/showthread.php?t=286602

The PC amber has such a wide distribution, why bother with red by itself?

I like the 15 n-w:3 PC amber:3 cyan distribution

 

[saabluster]

Seen this one?
http://www.candlepowerforums.com/vb/showthread.php?t=286602

The PC amber has such a wide distribution, why bother with red by itself?

I like the 15 n-w:3 PC amber:3 cyan distribution

Because the PC amber will not replace the red LEDs. I have done exactly what that link shows with rebels and I did not like the light quality. It was very peaky and made some stuff look real strange. It is better to just start out with a white LED and fill in from there.

 

[Th232]

Thanks for the replies guys, will definitely consider mixing in some cool whites with the neutral whites, haven't tried that before. Considering mixing some of the high CRI Rebels in with both neutral and cool ESs for the white section, bit annoying how the bin for the cool white ESs is still so broad though. Still, with the number of Rebels I'm using the law of averages should kick in. I hope.

Now to figure out how much of each I need (and find a source for the cool ESs). Or I'll just grab some regular cool white Rebels. 180 lumens at 700 mA is still pretty good.

 

[Linger]

Consider a wide selection of warm / neutral tints. If you read the spec sheet it'll indicate which numbers are higher CRI (iirc 350ma/70lum). Beyond that, you can mix in the higher efficiency (350ma/100 lumen) neutral bins. A single cool emitter goes a long way to bringing out the whites. And a heavy focus on the +/- 3500k rebels will dramatically reduce the role for filler red / yellow / amber, which should help with efficiency and make blending easier.

 

[blasterman]

will definitely consider mixing in some cool whites with the neutral whites,

Nah, this just gives you excessive overlap in the green-yellow region. Tried it before - didn't work - just made the light too 'lemon-green' colored.

IMHO, start with neutral rebels and build around them. Add a bit of cyan, then some red, and then just a bit of amber to compensate for any additional red you add.

What would be really cool is if you could add some far red rather than what is really orange-red (630nm), and then you'd really have a remarkable light. Given how difficult is it to get far red emitters it might not be worth the trouble though.

 

[Opto-King]

Just a refference of high CRI LED module used in medical applications:
http://www.optodrive.se/Pressrelease2.pab

 

[Th232]

Well, considering this is my first time with Rebels, I think it might be time to pull together an order from Luxeonstar to play around with. Given international shipping costs Future Electronics is out for now, so I'm planning to buy from Luxeon Star. So far my shopping list is one each of:

White:
4000K 85 CRI (144 lm @ 700 mA): LXM3-PW51
4100K 70 CRI (180 lm @ 700 mA): LXML-PWN1-0100
5700K 70 CRI (178 lm @ 700 mA): LXML-PW21
6500K 70 CRI (180 lm @ 700 mA): LXML-PWC1

Colour:
Red, 627 nm peak (85 lm @ 700 mA): LXML-PD01-0040
Amber, 590 nm peak (130 lm @ 700 mA): LXM2-PL01-0000
Cyan, 505 nm peak (130 lm @ 700 mA): LXML-PE01-0070
Blue, 470 nm peak (48 lm @ 700 mA): LXML-PB01-0023

Some of them I can't see myself using, e.g. I suspect that it's more efficient to use the LXM3-PW51s rather than fill in the 480 nm trough with 470 nm blues. Still, might be interesting to see the results.

Have I forgotten anything that might be really interesting in terms of colour or tint?

 

[Mark620]

What would be really cool is if you could add some far red rather than what is really orange-red (630nm), and then you'd really have a remarkable light. Given how difficult is it to get far red emitters it might not be worth the trouble though.

Do you mean Deep Red 655-670nm or Far Red 725-745nm?

 

[blasterman]

660-670 range given standard red LEDs are really orange-red around 625-630nm. No point going beyond 700nm, IMHO.....

 

[saabluster]

660-670 range given standard red LEDs are really orange-red around 625-630nm. No point going beyond 700nm, IMHO.....

Agreed. I have both deep and far red and the far red are definitely a waste of time.

 

[MikeAusC]

The portable LED lights I've seen on film sets here have a Colour Temperature Control so they can be used to fill in Daylight or Incandescent light - or anything in between.

They use about 200 5mm LEDs - an equal number of Cool and Warm LEDs - and adjust the balance between the two sets to change Colour Balance.

I don't have any work coming up, but I'll definitely get a photo of one of these units next time I'm on the set.

 

[Th232]

Minor update, got the LEDs in stock and reflowed them yesterday.

At work we have these neat containers (think they're for culturing or other samples?), and they're just the right diameter for holding a 20 mm star. Tape on the back of the LEDs is just there to ensure that nothing was bouncing around during the trip back home.

Also note the pin headers so that when I'm tinkering with everything I don't need to constantly solder and unsolder wires.

Now where's that block of Al gone...