Multiple array of LEDs to reproduce HID/incan lighting

Time for a new project

LED's have increased in lumen output significantly in the last few years, with some putting out 2500+ lumens per die (Cree XHP70), so I'm thinking about making some lights to mount on the front of our retrieve vehicles for late night paragliding retrieves… Yep, I know I should probably just go out and buy some HID's, but here in Australia a good pair will cost around $2000… Another option is some high power incan's, which is tempting (there's a good local manufacturer making quality housings running 250w globes that seem to be an excellent and cheapish option) but where's the fun in that

So my reasoning goes as follows;

1 - LEDs are putting out similar lumens to incan/HID lamps, but control of the raw beam seems to be the issue.

2 - TIR optics can provide good control of the output, but seem to be limited in size due to the inherent limitations in molding materials like PMMA.

3 - Diameter and depth of the optic/reflector has a direct, proportional impact on the size of the final beam size. At least this seems to be the case from reading multiple thread here on CPF, eg;

http://www.candlepowerforums.com/vb/showthread.php?278774-Reflector-characteristics

http://www.candlepowerforums.com/vb...Aspherics-Reflector-Throw&highlight=reflector

4 - Size of the die also matters if you want a small hotspot. Larger die = larger hotspot (see links above). Something I'm keeping in mind, though I actually don't want a super bright hotspot without a gradual spill—this is not great for use on a moving vehicle. So possibly a larger die led will actually have a nicer spill…

5 - All commercially produced lightbars (that target the 4WD market at least) look to be using off the shelf carclo or similar optics ie; small diameter optics. I've seen a bunch of these in action now and while good at producing a wall of light in close, they're pretty poor as long range spotlights.

6 - On the other hand, good reflector design such as in the SR95s-UT has an amazing beam—distance, spread, spill (or relative lack of) are all excellent for an led.

7 - Why are there no commercial 'lightbars' or led spotlights using this approach? I'm happy to run less, high power led's with large diameter reflectors if the output is sufficient. An array of (5-10+?) led's using 50mm, even 100mm reflectors surely must be getting close to something like a good quality pair of HID's? Is there some reason this isn't happening that I haven't thought of?

8 - I've had no luck in sourcing high quality reflectors (such as in the olight). TIR's are easy to source, but after seeing the olight in action, and lots of reviews/beam shots here, reflectors for long distance seem a natural choice. Where can I find quality reflectors?

9 - Before anyone gets excited, these will only be used in outback AU on remote roads. We've had a few accidents with hitting kangaroos at speed now and it's not pretty.

I'd appreciate any feedback or suggestions, particularly in relation to no. 8, so I can get stuck into some testing.

Cheers

Alex

Anyone with some ideas or suggestions?

Thanks!

Do you know what beam pattern you are looking for? Something like the degrees of the "full width half max" beam or something like that? That will at least help you select candidate optics or reflectors.

My experience is with making bicycle headlights. I based my desired beam pattern on commercial lights that I own, and ended up with a Ledil Heidi optic with a 8 degree beam, measured as full width half max. It's a pretty tight beam for an optic. I'm not sure how much tighter a reflector could be, although as a general rule, a tighter beam requires a larger reflector or optic relative to the size of the light source.

Part of the trick to finding a good optic or reflector is to go to the manufacturer's web site and look at their full product lineup. A lot of lighting parts suppliers will only offer a small fraction of what is available. For instance, Ledil's web site is www.ledil.com . Carclo and Fraen are also good sources.

Hi Steve,

Thanks for the response. Part of the dilemma is that there doesn't seem to be any optics/TIR's or reflectors aimed at led sources larger than ~30mm. What I'd like to try is (somehow) using leds as the illumination source in a large, automotive spotlight type reflector, to see if the result is similar to the hid/incan equivalent. If the lumen output is comparative, then why aren't they being used?
As for beam angle, to a certain degree narrower is better as going wide isn't the problem. So if I can get ~10 degrees fwhm, with a soft roll off through the spill, then I hope that would be sufficient.

Trying to think laterally;

What about using a reflector with a led in the typical position, then mount a small conical mirror facing the led to direct the spill light to the reflector. This might produce a cleaner, more efficient beam with less spill? (excuse the quick sketch);




Or using an offset parabolic reflector to shape the beam — led>TIR of appropriate angle>parabolic reflector;






Or reverse mounting an led inside a standard reflector, though heat from the rear of the die will be difficult/impossible to remove as it's in the middle of the reflector

It sounds like it should be simple, which makes me think I'm still missing something…

Cheers

Alex

my experience is that if you see a simple solution to a problem, and no one else has used that solution, you may not understand all the problems associated with that solution yet.

I think one downside of using a reflector with a big light source, and wanting to get a tight beam, is that the reflector is going to be rather long from front to rear. You might find a light that produces the beam that you want, measure the LED and reflector, and then scale up those dimensions based on your LED size. That'll give you an idea of the final dimensions.

You idea of using a conical reflector in front of the LED is reasonable, in my experience. There are optics sold that perform this function for smaller LEDs, sometimes for the purpose of using them in a reflector. The problems are fairly basic.. how to mount it and get it optically aligned, as well as where to get it.

Mounting an LED so it fires sideways in a reflector is done on a lot of bicycle lights, and works well. The section of reflector that isn't being used is just removed.

While I've spent a lot of time playing around with LEDs, optics and reflectors, and think that one or two experiments can teach you things that you won't get from hours and hours of perusing the web, there is something to be said for just grabbing commonly available 3W LEDs and the small TIR optics that are made for them.

Going down that path now - have ordered a range of optics and getting some proto boards made up. I'll post back here with observations

Thanks!

I hate to sound like a broken record, but go read about Etendue.

Beam control / beam angle / etc. is limited by source size and reflector size. Most of the light of a HID capsule is in a few mm diameter. As well, that light is predominantly 360 degrees (i.e. most of it will hit the reflector and be controlled). If you want the same 3000-4000 lumens from an LED array, you are looking at > 10 mm diameter in an array ... so your reflector just got 3-5 times bigger compared to HID. Unfortunately, all the light is coming out the front which means a deep reflector. As you discovered, you can angle the LED into the reflector, but now you have a different reflector design and still have your size issue and may have made it worse a bit to get good beam quality.

Semiman