Archive for February, 2017
It’s a provincial holiday here today, Family Day, and what better use of my free time is there but to dick around with the H4 leds some more.
One thing I haven’t mentioned before is my puzzlement with what the data sheet says. It states, and it does not specify if this is for the pair or a single, “input power L/25W H/25W”.
Ok then, let’s see if we can make any sense of that. On low beam only the cup shrouded led elements are powered up. That’s half of the available elements on the bulb. And on high beam all the led elements are powered. So how come the wattage figures remain the same?
I hooked a bulb up to a power source and ammeter. The current draw varied with input voltage. At 14V the current measured 1.20A. At 10V the current measured 1.10A. But curiously, at 11.5V the current measured 1.47A. My power source only goes up to 15.5V, at that setting the current was 1.10A.
That was for high beam, low beam values very similar.
So a couple of things strike me. One is that the current draw had a peak at 11.5V and dropped of on either side of that voltage. Must be something to do with the power regulating circuits in the bulb, I bet it’s obvious to those with a bit of electronic knowledge. The second things is that the current draw was pretty well the same for both high beam and low beam. So that goes a little way in explaining how the spec sheet claims 25w for both high and low beam.
But do my measured values even come close to the spec sheet values? Let’s take the 14V reading, 1.20A.
That’s a fair bit from 25 isn’t it?
Again it’s not clear if the spec sheet is for one bulb or two. If it’s for two then doubling measured value for one bulb would give 33.6W. Closer to 25W but come on…
At this point I get the feeling that either I’m missing something damned obvious or else the spec sheet is inaccurate.
As I had one of the led bulbs in hand I thought I’d try comparing it to a 55/60W halogen in a couple of 6.5″ e code H4 lamps. These are nice German made Hella lamps, new old stock, unused, meant for the Iltis military vehicle. I thought I’d shine the lamps onto a bit of black card and see what the beam pattern looks like at a very short projection distance.
Low beam, 55W halogen. Oh I have to add that the batteryused as power source wasn’t at full charge, it’s at 12V. And for some reason the halogen low beam is lass bright than expected. But it’s beam pattern I’m interested in.
And now high beam, 60W halogen.
You know it all comes down to the placement of the light emitting elements in the lamp housing. And to how the light disperses from the elements. I think that the led placement is fairly good, but I think (and talking completely without any direct proof) that how the light comes out of the led, how it radiates from the surface mounted elements, differs from how the light emits from a tungsten filament. It’s not an outlandish assertion, the halogen filament is held in space and radiates all around, 360 degrees. The led elements are constrained by being placed on a surface and the best they can do is radiate 360 degrees minus the amount the led back plane interferes ( and that’s assuming that the led elements alone radiate 180 degrees, and I’m not sure that they do).
Ok enough of this for now. I think the thing that will put this exercise to rest will be the side by side comparison with the halogen lights on good friend Simon’s van.
I’ve been trying out the led bulbs since I first posted about them. I still have the same opinion, low beams good, high beams meh. In rain, and in snow, I’m not seeing a much of a drop in the high beam performance though.
I took a little time tonight to take some pics with a 80/100W bulb in right hand side lamp and the led in the left hand side lamp. I couldn’t find a good wall close to home, I apologize for using that corrugated metal structure.
Ok, here we go, first up is both low beams on. Left is led, right is 80W halogen. Notice the halogen has more of the angled kick, better defined. The led not so much and there is a stray beam at a higher angle.
Ok now to a gently sloping downhill dirt road. Same drill, same comparison. You be the judge.
So what do I think? I want to like them, I really do. But I’d give them a 7.5/10. I’d like them to be brighter. And I also have the suspicion that the led element placement that I showed in the original post is not quite right (as compared to the filament position in the halogen bulb). I might take the time to play around with a spare lamp and and bulb, on the bench, and see if some adjustment to the bulb projection into the lamp has any effect.