Halogen Headlights

[PeterZRH]

LEDs with outputs up to single digit watt ranges might get 100 lumens per watt (or maybe up to 150ish today) but you can pretty much halve that for those used in high powered applications like car headlamps. The thermal junction temperature totally destroys the efficiency in a spectacularly non-liner fashion. This is pretty much a given where packaging is tight such as in a car.

In fact they are very probably less efficient currently than xenon or other gas discharge technology. The reason for LEDs vs xeon is cost and simplicity both in manufacture and the fact they don't require a 600v ballast/inverter. Far more durable and easier to handle at too, while still giving the higher colour temperature. At the lower end of the second hand market, I'd actually regard xenon lamps as a negative feature, especially on mass market cars.

I wouldn't write-off halogen yet. The vast majority of new cars still rely on this technology and probably will for the foreseeable future. You can even improve the efficiency by running them "hotter". This is (at least was until LED technology came good) common for bicycle lights - running a 12V bulb at 13.2 or 14.4V. Philips sell the xtreme-vision range which pretty much do the same thing at 12V. You lose of course in bulb life.

I discovered the car I bought had been converted and I can't say the headlamps are that noticeably inferior to my 2013 VW other than the less focused hot-spot. I fact my P6 headlights are hugely better than those of the 1998 Audi A4 I had before (which for some reason were spectacularly bad).

I'd rate the headlamp upgrade as top of the list of P6 improvements.

 

[Willy Eckerslyke]

I need to do a proper test, but I have a bright LED torch that seems to chuck out a similar light to one of the halogens I fitted to the P6.
It's a JetBeam Jetbeam DDR26 that claims to put out something like 1000 lumens. I found that it's enough to drive by - on the private lane up to my house.
On the basis that it doesn't get as hot as a halogen, I doubt if it would be less efficient. Or am I missing something?

 

[chrisyork]

Big problem with LEDs as far as cars are concerned - so far - is that nobody seems to have developed a reflector or bulb shape able to focus and aim them. So you might get a huge amount of light, but it isn't necessarily heading where you want it to.

I'm with the other contributors here in thinking that halogen remains the most usable and practicable technology at the moment.

Chris

 

[PeterZRH]

Nah, you can't compare really. An LED torch looks brighter by virtue of colour temperature. It might well be that in a small, concentrated area it is as bright but headlamps have a huge flood/throw pattern.

Then you've got the claims which are usually based on the best figures of the LED die makers. Trouble is, as part of the manufacturing processes LEDs are sorted according to efficiency (or "binned") and those on the mass market are usually a good 20-30% off the optimum. The best are sold off at a huge premium. That's before you get to the much larger, more efficient reflector on a car and cooling issues with compact LEDs.

I have an bike light with a Seoul P4 and it claims "1000 lumens". I'd say more like 700 at about 9watts with a large, external lithium battery pack. So that's less than half a single dipped headlamp bulb and well under 100 lumens/watt. Damn bright though.

Also, I have a hand torch powered by an 18650 lithium cell claimed to be 800 lumens, which might be true if you drove it with something more than that single cell and fitted a large heat sink; call it 300-350 real world. So 1/5 of a headlamp. Petzl headtorch is around 80-100 lumens.

Any compact hand flashlight powered by conventional batteries (not lithium) is likely to be 150-200 lumens range, unless it's one of those crazy maglite mods.

I'd be very surprised if that flashlight made anything like 1000 lumens. Doesn't take away from the fact they are shed loads better than anything that went before, it's just that manufacturers claims for these things are almost always pure fantasy.

 

[PeterZRH]

Big problem with LEDs as far as cars are concerned - so far - is that nobody seems to have developed a reflector or bulb shape able to focus and aim them. So you might get a huge amount of light, but it isn't necessarily heading where you want it to.

I'm with the other contributors here in thinking that halogen remains the most usable and practicable technology at the moment.

Chris

Exactly, which is why we mostly see them currently as daylight running lights. The color temperature makes then stand-out and "be seen" but they don't need to be focused "to see". (same story with brake lights).

Halogen is cheap and very effective.

 

[Willy Eckerslyke]

Things are moving seriously fast though. The torch I mentioned has a Cree XM-L T6 (& 18650 lithium) which is supposedly a fair bit brighter than the older Seoul P4. Give it a couple more generations (5 or 6 years) and I'm sure emitters will be up to halogen levels.
As for reflectors, they'll clearly need something specifically designed for them, but it's not rocket science.

 

[rockdemon]

On bicycles the high power leds have really improved. Give it time and they'll get there.

 

[PeterZRH]

The main problem is that LED dies are by nature flat as opposed to a blub. i.e. the light is scattered only forward in a (wide-ish) cone. If you think of the shape of a conventional reflector this means only a small part of it actually can be used effectively. A bulb can sit more or less at a "focus" of a reflector and give a quite well controlled beam pattern. That's not an issue that's going to change fundamentally, just how cleverly it can be engineered around.

You could use lenses to focus but these will create halos and reduce transmission efficiency. You could mount a die backwards but then you get dark spots due to the shadow.

I actually built my own high powered bike lights years ago before the commercial offerings were anywhere near as good as now and spent ages reading through candlepower forums (I think). Now that was a geek-fest if ever there was one full of useful info though. Now bikes are really one area where lumens/watt are king. A few 10s of watts in a 120kW car is neither here nor there ultimately.

But I suspect you are right it will probably happen and I certainly wouldn't swap my LED flashlight for one with a filament lamp which will give 20-30 lumens.

 

[Willy Eckerslyke]

... spent ages reading through candlepower forums (I think). Now that was a geek-fest if ever there was one full of useful info though.

BTDT!

Now bikes are really one area where lumens/watt are king.

Another being underground exploration and photography. Welsh slate swallows illumination very effectively and some of the chambers are 150ft high...

 

[Vern Klukas]

The main problem is that LED dies are by nature flat as opposed to a blub. i.e. the light is scattered only forward in a (wide-ish) cone. If you think of the shape of a conventional reflector this means only a small part of it actually can be used effectively. A bulb can sit more or less at a "focus" of a reflector and give a quite well controlled beam pattern. That's not an issue that's going to change fundamentally, just how cleverly it can be engineered around.

You could use lenses to focus but these will create halos and reduce transmission efficiency. You could mount a die backwards but then you get dark spots due to the shadow.

I actually built my own high powered bike lights years ago before the commercial offerings were anywhere near as good as now and spent ages reading through candlepower forums (I think). Now that was a geek-fest if ever there was one full of useful info though. Now bikes are really one area where lumens/watt are king. A few 10s of watts in a 120kW car is neither here nor there ultimately.

But I suspect you are right it will probably happen and I certainly wouldn't swap my LED flashlight for one with a filament lamp which will give 20-30 lumens.

Rather than a reflector/lens combo and just a few LED chips, the approach the auto makers seem to be following is scrap the point source/reflector approach and use many LED chips to build effectively a mass array shining forward. See Audi's new lamps on their flagship A8, which are controlled and can illuminate individual portions of the roadway at will.

Yours
Vern