LED lightboards

[Volvo farmer]

I got a few of these boards from Tom Woods when he mentioned them in here. Ordered a bunch of 2000mcd LEDs out of Hong Kong and built up my first board today. These suckers are BRIGHT. I put one on a 12ah sla battery and stuck it on the counter in the john and closed the door. There's enough light reflected off the ceiling to comfortably take a whiz in there. Maybe not quite enough light to shave but still quite impressive.

If I adjusted the regulator conservatively, I was only running 45ma. Wide open, it sucked about 160MA at 12.75V but that might be too much current for the LEDs to last. I saw very little difference in brightness from 50ma to 160ma.

Here's some pics

[cdg378]

LED lighting is very impressive, boat owners have been into this for quite some time even using red LED's.

I am working on a system that uses AA ni-cd's and cat 5 computer network wire along with small solar cells that paste into the tops of the windows of my boat to recharge during the day along with a small savonious farm mounted on the top bulkhead of the boat.

Very promising, cat 5 will carry the LED load for reasonable distance, also instead of dimming through mofset I am experimenting with just lighting some leds and then more leds with multi position switches.

If you come from a well ligthed room into a led lighted room you will think that it is dim but out on the water at night it is dark all around so any light seems to be bright. Let your eyes adjust and you will get that shave without cutting your head off! :0)

[pyrocasto]

Are those really only 2000mcd, or are they 20,000mcd?

I've got 10 20,000s that I want to use, so I was thinking of using the led board.

[Volvo farmer]

Ooops, off by a degree of magnatude, that's all. Yes they're 20,000 mcd. Good catch!

[ghurd]

Remember the MCD rating is a function of the viewing angle.

A wider viewing angle will mean less MCDs, but often a more useable light output.

A wider angle will generally increase efficiency and total light output.

Keep them under 18ma and they should last many, many years.

The light per amp goes up as the amps go down. The best bang-for-the-buck is around 3-5ma.

G-

[Barnac]

Hi,

I am the only one, I can't see your pics. and I would like to !

barnac

[ghurd]

Try here. Under lightboard rev2.

http://www.fieldlines.com/user/Tom%20in%20NH/files

[Volvo farmer]

Oooh, this is news to me. I wanted to use these as under-cabinet lights but they appear to be much too focused for that. I thought MCD was only a function of brightness and did not realize that the viewing angle was also affected.

Any idea what range of MCD I'd want for under-cabinet lighting? Is there any way for me to learn more about MCD-vs-brightness-vs-viewing angle for ultra bright white LEDs?

Your 18ma and 3-5ma measurements are beyond me. Per 4 string w resistor? per LED? Per 40 LEDs? Sorry to be so dense but this is new territory to me.

Thanks,

Bob

[ghurd]

Not sure where to start...

There is only so much light in a LED. Like a flashlight bulb, out of the flashlight shines everywhere, just not far, and not "bright" in any one spot.  In the flashlight, it is not really any brighter, just all the light is focused into a single spot.  The tighter the focus, the higher the MCD meter goes!

(take the MagLight outside, at the widest beam, how far can you see?

How far can you see with the tightest beam?

That's MCD vs viewing angle in a nutshell. The math is complex.)

I would look for 4000 or 5000 MCD and 50 to 70' angle. Thats what I use mostly.

They could be hard to find and not cheap. They tend to be less 'blue' and more even.

Standard viewing angle is 20'.

Honestly, 20,000mcd sounds like a 7 or 10', maybe 15' viewing angle. And that is probably "best of the bunch" instead of typicial MCD. There is a large variation even in the same lot.

The amps per LED will be the same as the string. 25ma is usually OK for short time use. 20 is better and usually where the ratings are set by honest companies.  The perceived brightness between 25 and 18ma is very small, but the power percentage is large. I make most of mine for 15 to 18ma, and many are on all night every night for several years now with near 0 failures, and I make thousands of them.

About the 3-5ma.  Some people want to turn off half to dim them. It is much better to lower the amps and leave them all on. 8ma to all 40 LEDs is probably about as bright as 20ma to 20 LEDs. Don't recall how that board is set up.

LEDs wear out by power^2 X time = shot. (made that up just now, so you get the idea)  Lowering the amps a little will very greatly extend the life.

You can E me if you want, myusernamehere at neo.rr.com

G-

[Tom in NH]

The LED Lightboard's light is more like a reading lamp than it is like a florescent lamp because the light is focused to a pretty tight spot.. You can widen the spot by judiciously bending the leds so they point in different directions. Several boards chained together helps. You can find LEDs which radiate light in a wider angle. I haven't experimented with this yet, but I would imagine reflectors and diffusers would be very helpful, maybe not for under counter lights, but for other applications. --Tom