LED headlights - be advised...

[TylerDurden]

Edited for updates:

I popped for a 40 buck set of Rolinger 5000lm of LED bulbs on amazon.

Installed into MK2 Jetta.



The low-beam uses the two emitters near the shroud and the high-beam uses the two emitters closer to the flange.

The emitters are very bright, but the throw of light has some dark areas, and the shroud molded into the LED fixture may be obstructive, as well as the emitter position may be out of the sweet spot. The fixtures can be rotated, but proper depth into the stock MK2 housing is still a question.

I'll post here, as I explore if these LEDs are useful without too much fiddling .

[TylerDurden]

It seems you get what you pay for...

The low beams have a fair amount of scatter and there is a dark region in the center of the high-beam throw.

Note the shroud on the LED fixture and the distance of the emitters from the flange (reference plane)


The shroud on the LED may not be needed, considering there is none on the stock 9004.

The filaments on the stock 9004 bulb are positioned 44.5mm from the flange (reference plane), whereas the LED emitters are 41.0 and 35.5mm (lb/hb) from the reference plane.



So, the LED emitters are well behind the focal point of the reflector, causing the scatter on the low-beam and a dark center on the high beams. I'll try to shoot a demonstration in the next few days.

I'm not finding many 9004 LED units with adjustable focus, and the ones I find are pricey. I'll look into modifying these, since they are so cheap and simply constructed.

[TylerDurden]

OK, here's what happen when you back a bulb out of the focal point... the beam spreads out, duh.

The white panel is about 9 feet from the front of the car, with one tungsten headlight only. (Tungsten, since the LEDs are too short.)

First is the low beam, in the correct position, then backed out about a quarter inch. 2x
The view jostles as I switch to high beam, and repeat the in-out. 3x

(looping gif)

So, you can imagine the spread and scatter at driving distances... not so good, if the light source is out of the focal point.


Looking at the switch to high beam, it seems more than just an increase in brightness, the beam seems higher... so maybe the shroud on the LED might be worth keeping.

Here's a diagram I found on a Porsche site, showing the effect of the shroud in an H4 setup.

1)Low emitter, 2)shroud, 3)High emitter

It might be possible the designers used the high-beam filament as a de facto shroud to keep some light off the bottom of the reflector... it is noticeably larger and directly below the low-beam filament:



I have an idea about hacking the cheapie LEDs, I'll post later in the week if time permits.

[TylerDurden]

Update:

Some more exploration reveals that the LED units easily come apart to modify. The larger ring part could be modified to sit further away from the emitters and place the light source at the focal point.



But rather than modify the part itself, maybe make a new one:

You can see a beveled recess that allows the ring to slide back onto the base of the LED.

The public library here will print 3D files for free (pay a few cents/gram for the plastic).

I left a little too much space in the center bore, trying to correct for some plastic shrinkage, so a couple of wraps of teflon pipe-tape on the parts (narrow sleeve and body) made for a firm slip-fit. (That tape might actually help insulate the plastic from the heat. I'll check them occasionally to see if the plastic is getting heat distortion.)

Installation is pretty easy.


I added some extra space on the recess to fine-tune the focus, and wound up using it all. The high beam still has some spread because the emitter is further back than the low-beam emitter, but the low beams actually now show the sloped cutoff line, which I don't think even the tungsten bulbs did very well.
Low Beams


High Beams

(They truly are brighter, but the cell-camera auto-exposure "corrects".)


Color compared to tungsten (engine not running, so ~12V, not 13.5V)


Much brighter on the road, too.


So, for cheap LEDs, they work ok now. Which might be just as well, since there's no telling if more expensive ones have similar issues.

[Fatmobile]

Nice writeup. Thanks for posting it.

[greg lousy]

yeah thats a thorough presentation, thanks