Researching LED's as powerful light-source

[HanClinto]

Okay, I was talking alot about this in the main thread, but I thought to bring it out to its own area so we don't clutter the main flow of thought. I hope that other people out there are currently as obsessed with LED's as a light source as I am.

(Note: This assumes you've read Dec 15-17th in the main DIY Video Project II page)

So after researching 1157's, I was told about a new sweet LED called a Star-O

I just skipped more studying for finals to research these things, and they're pretty sweet.

180,000 mcd with a 10 degree beam width... pretty impressive, and only for $16. Just for comparison, the 1157 LED cluster is 78.720 mcd with a 12 degree beam width.

From my calculations, it seems like it would be cheaper to get the 1157's than the Star-O's -- the Star-O red's are about 5-8 times brighter than the white stars... from my calculations a 180,000 mcd star-o with a 10 degree beam width is 4.3 lumens. A 78,720 mcd 1157 with a 12 degree beam width is 2.71 lumens. At $16 for a white star-o and $7 for a white 1157, I get $2.58 per lumen with the 1157's and $3.72 per lumen for the star-o's.

So roughly $2500 to get the cheapest possible 1000 lumen cluster of LED lights (but then you have to focus them all, but I like the fresnel lens cluster sheet to solve that problem)

However, I'm pretty new to all this, so I might be wrong. The formula I used for mcd to lumens is:
( 1 - cos(beam_width/2)) * 2pi * cd = lumens

Not sure if I'm right on all this, but it seems within the right order of magnitude.

However, if they ever come out with the a new star-o that's brighter, that would be incredibly sweet.

Anyway, as far as my own progress goes, I just got a nView Z-Series 640x480 32bit color transparent overhead LCD thingy for $60 off a friend. Works fantastic. I still ordered a raw LCD with controller board so that I can build one the DIY way, but for watching movies over Christmas break, I think I'm gonna' do the old OHP thing. Should get me going for < $100 . I'm still anxious to build my smaller, cooler (temp-wise), quieter, and cooler (geek-wise) LED-lit projector.

--Clint

[halojoy]

white LEDS are an intweresting alternative to
light bulbs

the angle of the light spreading is a key issue

[HanClinto]

Yes, I know I just used l33t sp34k in the post subject, but in this case I believe it applies.

I was told to research Star-O's, which are marginally cool as explained in my last post. HOWEVER, the same manufacturer also makes 5 watt LED emitters. I saw that they only appeared to be available in red, orange, and blue, yet I checked the price list on a distributer's page and they're available in white.

Part#: LXHL-LW5C
Color: White
Radiation Pattern: Lambertian (basically straight-out directed beam)
Color Temp: 5500k (is this good/bad? I don't know anything about color temp.)
Typical Flux (lm): (I'm assuming this is lumens, that's what came up on a google search for the abbrev. for lumens)... get this.... 120 lm . w00t!
Price: $43.20

So that means an incredible price of $0.36 per lumen! (as opposed to $2.43 per lumen on the best thing I found before)That means a 1080 lumen LED array of 9 emitters would cost approx. $388.80.... WOW. Keep in mind these things DO need heat sinks I believe, but still. They've got a metal board on the back that the heat sink attaches to. Just heat-compound them to a solid metal plate and then cool that puppy off with heat sinks on the other side... a couple silent computer fans and you've got a SMALL (3*14.5mm = 1.71 inches per side)... so smaller than 2" by 2" 1080 LED projector.... w0w. I'm in shock.

Anyone else as excited about this as I am? I guess I better give you guys the links before you kill me.

Mark Hannah Surplus Electronics

Spec Sheet for 5 Watt Emitters

Current things I do not know:
The beam spread on the emitters... I couldn't find specs on that for the *white* emitters, although since they're in the same housing as the normal emitters, it looks like it's a viewing angle of 110 degrees, or the included angle (where 90% of the light is) is 150 degrees. This actually works quite well, as we could have the lights very close to our fresnel lens... wait. No fresnel. We could use real optics here! Wow. Nice when you're dealing w/ small sizes. A heck of a lense to make a 110-150 degree spread of light go paralell... that's a high power lens.... but we could find them... and if they're smaller, they're cheaper! Wow. The $43 per emitter is still huge for me as a college student, but I might just ask for some of these puppies for Christmas. Wow they're cool.

Keep the wheels of imagination chuggin' and spinnin'.

--Clint

P.S. Hah! I just read in the .pdf spec sheet in a side advertising note about possible uses... at the VERY bottom of the list of advertised possiblities is "LCD Backlights / Light Guides".... it seems that we're not the only ones considering the project option.

[remp]

Hanclinto

There is one other interesting thing about solid state emmiters like LED's.

You can pulse them.

As an example I have an led emmiter assy pointed down my drive with the receiver in the garage and sending signals into the house. If a car drives down the drive we get a buzz.

Thing is the drive is 30 metres long. Unpulsed led only gets to about 10 metres max. Pulsed it easily gets the 30 metre rain or sunshine.

They are cheap led rated at 100ma. Pulsed they get 1 amp for a tenth of a second.

I think you could probably double your apparent light output, possibly even much higher by pulsing them and if you pulse at say 100 pulses per second you will be well above the flicker rate.

The human eye if it sees a light will continue to see it for a period of time, even if the light has long gone. Persistence of vision.

Might be useful

[HanClinto]

VERY interesting.... do you think that continuously pulsing an LED would overload it's max amperage rating? Or is the startup current included in all of that max-rating stuff?

Very neat stuff to think about. I'm trying to see what kind of lenses I would need right now in order to condense everything here... the incredibly cool thing about having a 2x2 inch light source is that you can use solid-lens optics rather than fresnels. That excites me.

--Clint

[remp]

Its a solid state device. Lots of solid state devices get pulsed every day. I would imagine as long as you stay within the maximum dissapation ratings it would be OK. Probably need to look closely at the data sheet.

Your main problem is going to be combining the output of X number of emmiters into one beam. You might be able to do it by aiming them all at a parabolic reflector, and collecting the output at the focal point.

Also many high output white LED have not much green content in the light. You need green. That has been posted before. Might show in a search Video projector part 2.

green and led

Maybe you could construct a white beam from regular red,green and blue led's and pulse them to very high output. Perhaps a thousand at 10 cents each or less. Thats only a hundred dollars.

Hope this helps.

[UrSv]

Remember that when pulsing the light source this might also be interfering with the refresh rate of the displayed image and if they are not exact multiples (with the light being much higher frequency than the image refrash rate) you might get some pretty strange effects going on at the screen. For normal bulbs I think this is taken care of by the inherent slow nature of the on/off characteristics. For LEDs this is almost instant. Try it first.

/UrSv

[HanClinto]

Originally posted by remp
Your main problem is going to be combining the output of X number of emmiters into one beam. You might be able to do it by aiming them all at a parabolic reflector, and collecting the output at the focal point.

Actually I think that's probably the easiest problem to solve here. This is not my original idea, although I think it's a fantastic way to combine several light sources easily. I realize that you'd want to get these emitter assemblies as close together as possible, or you could use something like this fresnel array to combine it all together.

P.S. Why can't I do IMG tags correctly? That's bugging me.

[alvaius]

The 5 Watt Luxeon whites are only rated for 1,000 hours at this point. It will be mid-2003 before they have an extended life. For luminous efficiency, using RGB side emitters into a backlight diffuser plate may actually work well. That would allow full color control as well and make for an easy OHP configuration.

Alvaius

[HanClinto]

Alvaius, do you think it would work to do a combiner... like get an old set of beam-splitting optics and run it in reverse? Put in the three colors and get out white? Then use that as your light source? I would think you'd lose too much light with a diffuser... but maybe I'm wrong.

I'm a little confused as to what the difference is between Side-Emitting and normal luxeons. Can you explain the difference to me?

Thanks! Keep up the great work guys.

--Clint