LED Headlight

[Tweety]

I think you are missing one of the fundamental principles here to get this working... (No, I'm no expert, but I know something not mentioned in the thread...)

With the incandescent light the direct light from the bulb out through the headligth is used for near lighting, ie the part of the beam directly in front of the car... The reason is that the distance from the bulb to the lense (glass in front of the headlight) is short... The light bouncing of the back wall and being focused has much longer distance to the lense and just like with a pair of binoculars you can then focus them a lot longer ahead of the car...

The difference between high/lowbeam is the same principle... The lowbeam is a filament closer to the reflector, with a shorter and wider beam (still with two parts) the highbeam is a narrower filament, longer from the reflector... That means the near lighting is worse (weak, scattered) but the longer focus means you get a good long distance beam... Usually the bad near lighting of the highbeam doesn't matter since usually the lowbeam stays on and you just add the highbeam to throw the light further at the same time...

The problem you guys need to solve is that the LED's have a very, very short range on their own... Not even close to the lowbeams range... If you look at captainslugs images above, the spot in the middle is the light of the sides of the bulb being focused in spot that further away becomes a wide cone of light...

Take the same images and put the wall at twice the distance and the LED's will fail to light it...

I can tell you without experimenting that the small round LED's will not work in any headlight, what-so-ever unless you create a whole array of mirrors, prisms and replaced the front glass completely... The amount of lumens or mcd is irrelevant as the range of the focus is to short...

The larger LED's like the Luxeon Star come with a lense that focuses the light... Stick another lense in front of that one and re-focus them, and use say 2-3 of them as near lighting and 3-4 as far lighting and you could potentially make a decent lowbeam out of it... The reason being that you actually have the space to make a prismatic lense fit in the headlight housing to focus them... I'd say that would be a far better idea and probably less costly as well...

[Christ]

Can it really cost less than about $13 per headlight?

[Christ]

Originally Posted by wagonman76

That's something I'll have to play with. I'll probably just build the LED board, cut open a headlight case, and hold it outside at different depths in the case to get a rough idea. See how it compares with the headlights of my other cars. Then make an adjustable bracket to mount the LED board to the back of the case. Then when done I can aim each LED board so the brights and dims line up correctly to each other on a wall 25 feet away. Then there should be no more adjustment needed to the LED boards. I would think most of the light should go directly forward, since with incandescents you shine them on a wall to aim them and they do make distinct lit areas.

I think if we get something close it should be fine. There is quite a difference in headlight visibility between different vehicles.

I was going to suggest duct taping a cardboard surround on the lens (behind it) and manually moving the panel in and out to get the proper focus on an object of equal distance to the low beam focus on your car currently, then do the same for the high beam, and measure the distances, then if there isn't enough material to mount the LED's as far back as they need to go, you can make a plastic surround to mount it to.

[wagonman76]

I got my leds in the mail yesterday. I did a little digging on ebay and found the same thing cheaper. 500 leds for $30 including shipping. Enough for possibly 4 headlights plus a bunch to play with. 3.3v, 20ma, 18000 mcd, +/- 20 degree viewing angle.

Last night I did some messing around with them. I've got an old military power supply that my cousin gave me many years ago. You can use different combinations of terminals and get several voltages from 1v to 25v. One set of terminals gives me about 14.7v which I used. I've also got some leftover 330 ohm resistors from a TI85 serial cable I recently built.

I wired up the leds so they all faced very close to the same direction, sticking right off the power supply.

Initially I tried filing one flat on the end, and that pretty much killed the output. I tried polishing the flat surface back smooth, but that only helped a little. Looks like the best thing to do is leave them as-is.

First I used 2 sets of 4 leds each in series with a resistor. Only makes for 5ma current, of course they didn't even heat up. They were very bright. Then I removed one led each for 2 sets of 3, 15ma current. That made the total even a little brighter. I could feel a tiny bit of warmth above them on my palm after running them a few minutes, but the leds themselves didn't feel warm. Then for kicks, I pulled the resistor and they did get warm very fast, of course, and didn't even seem as bright (was probably killing them).

With the 2 sets of 3 (6 total at 15 ma), I could see it reflecting off a snowbank 100 feet away, and off the neighbors 911 sign about 180 feet away. The beam spread was pretty decent, and if you turn it a bit, there was a definite cutoff from the blinding zone that would come in handy.

I'll make a bigger array pretty soon and I'll leave some space behind them for possibly needed air circulation. Considering the 96 or so leds I figured earlier per light, so far it does look pretty promising for at least a driving light. Then I'll play with the headlights and see what happens. Even if it doesn't throw good enough for a high beam, it might make a pretty decent low beam.

[Christ]

Around here, low beams are called "city lights". We only use them in the City, or when cars are coming in the other direction and you're not on the outside of a corner (We don't bother if we're on the outside of the corner, because they don't affect the other driver at all.)

Anyway, the point is that in the City, when there are street lights, headlight output is really a moot point, at least for us country folk. We can see fine w/o the lights, they're more to let other drivers/people know where we're at. That means that if they're low-beam only, I'd be worried more about making sure they were sufficient for others to see them, while still being able to light up areas that street lamps don't normally light up well enough.

[Nerys]

Hmm that does bring up an interesting point. Dual head lights. LED's that don't really provide much light but in areas where you do not even really NEED headlights it would be fine. Then regular halogens when you DO need the light to actually see. That could work as a cheap temp measure to cut power usage.

also go with the 4 led's man. Trust me. White LED's do NOT tolerate heat. anything over 100' begins to harm them.

think about this. you are 98' so in order for something to be perceived as "warm" to you it has to be over 98'

this means if you perceive warmth YOU ALREADY RUNNING THEM TOO HOT :-)

go with the 4 per and just use "more" led's to get the luminance you need I might even go 5 to "under use" the led's and extend their life and tolerances even more.

[meelis11]

LEDs should not go hot if you use proper size resistor - just need bigger resistance when you use less LEDs in series. (google "led calculator")

[Nerys]

This is not correct. Well it depends on what you mean by PROPER resistor. You can resist for rated output (they WILL over heat) or you can resist for heat control.

If you run them at their RATED output they will over heat without adequate cooling. For passive cooling 9 cm/2 per watt of consumption is usually what is suggested.

thats why I suggest running them for heat control resistance NOT rated output resistance. IE add more LED's so you are under utilizing them and therfore eliminate cooling issues.

you need to run them for at least 30 minutes AT 90' F and see how hot they get. They should not get hotter than 95' to be safe (this assumes a hot summer day)

I tried to arrange it so my led's never run more than 5' above ambient in the hottest weather I am likely to encounter.

[winkosmosis]

Originally Posted by jonathan150cc

When dealing with LED headlights in general, why not aim the diodes away from the road, bouncing them off of a highly reflective rear cover that would work as a diffuser and an aiming mechanism. It seems to me it would limit the problem of being a very directional light. Enough LEDs would give very bright light while also being diffused and spread out over a larger lighting area area, like a standard filament bulb.

The design would be something like that of high beams on a tradtionally lighted car.
/ --------------------
l D )-------------------
\ -------------------

Something like that....

The "D" would be the LED while all other symbols would bascially be mirrors...

Plus I think if the reflector is shaped properly it would reduce the chance of someone looking at an LED. You have to keep in mind, you can't directly look at an LED. The light source is an exposed tiny point with a lot of wattage being emitted, which then becomes focused on a tiny point on the retina, creating burns. The same thing applies to poorly aimed HIDs.

[Nerys]

ahh no that is pure intensity and the deception of clarity. ie appears clear so people tend to "stare" longer before they realize "bad idea"

the led light comes out in a "cone" of brighteness. you would have to be pretty darned close for it to do that and if your that close you have other things to worry about.

Even a normal piece of head light "glass" in front should provide enough diffraction to keep this from being a serious problem. Though I have to say I never tried to put some many led's in one spot.

at those prices your starting to make me curious enough to make a go of one :-)