Technical data needed

[Silver Surfer]

Hey guys i am contemplating a halogen to LED conversion and need some technical data on LED's. right now i am think about using a few 5 watt luxeon LED's to get the job done. (if you know of something better, and by better i mean more lumens per watt, then please let me know). also do those luxeons come in different beam widths/focus angle?

specifically and need to know the voltage drop (so i can design the all so important current limiter).

thanks for the help!

 

[the_beast]

In terms of lumens/watt, the LuxV is probably the best there is when looking at the 'high power' leds. It is way behind some of the smaller 5mm leds however, but they won't really be of any use for you.

The LuxV is also a winner in terms of lumens/size - it throws out a lot of light from a small package. But they are relatively expensive in terms of lumens/dollar, so you might want to re-think the idea of using a couple. Basically what are you going to do with them? If you need a light to throw well then a Lux3 would be better as they will focus better, and if space is not a concern then 2/3 Lux3s will be cheaper (but take up more room and be less efficient).

As for voltage drop - that depends on the exact leds you get. They are 'binned', or separated into groups of leds that have about the same voltage drop. You need to know the bin of the leds you want to use. LuxVs range from about 6v to 7.5v or so, Lux3s from 3v-4v. You really want to drive them with a constant current source though (not constant voltage), as the Vf is likely to drop over time, which will put up the drive current and hence cook the led if you use constant voltage. By using constant current drive it doesn't matter so much what the Vf is.

Hope this makes sense. If you let us know more what you want to do with the leds then we can try and give more specific help.

And welcome to CPF!

 

[Silver Surfer]

Beast, thanks for the reply that is indeed helpfull. basically the plan is to replace the headlight on my dirtbike with some shock proof LED's. i am really concerned with brightness, throw and focus pattern.

you mention constant current. that is going to be a problem since the lighting coil output volt and amps will vary with RPM's. its a 12v system and the stock halogen is a 35 watt unit.

i have seen some simple current limiter designs that use a 7812 regulator chip...

.........................OR............................................

but i figured, why build a current limiter, just series about 4 LuxV to achieve the current limiting (assuming about 3.4v drop), and get more light. its a win-win situation. so if i am only investing in about 4 LED's then dollars/lumen isn't really a concern.

also, are you saying you can over volt LED's without concern as long as you watch the current?

also the Lux K2 look very attactive. 130 lumens and a Lambertian pattern (probably wont need a lens?).

 

[idleprocess]

You can't treat LEDs like light bulbs.

LED's don't limit their own current very well unless you have a precision voltage source... but given the tendency of Luxeons to drop their Vf over time and their variable Vf, this approach is not used very often. You also mentioned variable voltage from the bike's alternator - odds are that you'll kill the LEDs in short order without some sort of regulation. A voltage regulator is cheap relative to the LEDs, and many can be used as current supplies.

You're also going to want some optical device(s) to focus the LEDs' output, be they reflectors or some of the many specialized optics available. I'm sure you would find the unfocused output from LEDs both unsatisfactory and dangerous when operating a dirtbike at night. It will also be quite a challenge to devise an array of LEDs to simulate the beam pattern from your existing headlamp - it's doubtful that you vcould just cluster them at the base of your existing reflector assembly and get a useful beam pattern.

The Luxeon V "portable" is only rated for about 500 hours' operation. They often last much longer than that, but many have reported signifigant performance degradation at that point. Instead of looking at the (currently) hard-to-obtain K2, why not look at the readily-available Luxeon III star? It will be easier to work with star PCBs than bare emitters, and a number of optical solutions on the market are meant to work with star PCBs. Also - you will pay a premium in terms of cost and emitter lifespan for efficiency if you use the Luxeon V, but in your application, space and power efficiency don't seem to be critical; you could just use more emitters for about the same price and light output.

 

[greenLED]

I'd discourage you from doing this replacement. LED's don't provide enough contrast for you to navigate properly at night at dirtbike speed. From a safety perspective, it'd be a dangerous thing to do (and probably against some type of vehicle regulation in your jurisdiction).

Not only that, but focusing a single LuxV to give a tight beam is hard enough - I don't think anyone's found a solution for focusing *multiple* LuxV's (which you'll need to generate the same amount of light as the incandescent source you're wanting to replace). LED's are simply "not there yet" in terms of the amount of light they can generate (compared to incandescent light sources).

Have you looked into HID replacements? You'd probably need to replace the reflector on your headlight, but you'll get more light more efficiently with HID's.

 

[the_beast]

If you are looking to upgrade the (reasonably) bright halogen on your dirtbike I would say the best bet is the HID upgrade mentioned by GreenLED. You would really need a few LEDs of different bins (for good colour rendition) and some decent optics arranged to both throw and flood for good overall output to see where you are going. LED light tends to be kind of 'flat' so isn't great for navigating with, especially at speed.


As for the cost - if you invest in 4 decent LuxVs you will spend $150 before looking at optics and a mount etc. The HID will probably cost a similar sum (although to be honest I have no idea how much they cost and have no experience with them) but will be a better solution. The Lux3s are much cheaper ($10 each) with the K2s cheaper still, so much better option. They also throw better than the LuxVs and have longer lives, but output less light overall.

As for the regulator - constant current sources are just as easy to setup as voltage sources, especially if you don't have to worry too much about size and losses in a sense resistor. They can also ve built cheaply - no point in risking losing $150 of LEDs for the sake of a $10 regulator! As stated above - LEDs do not self regulate - instead they do the oposite - if you feed them more voltage they draw more current, get hotter and very soon they pop. Which can be very costly!

Not to put you off from the LED route though - red Lux3s would be an excellent mod to your tail lights...

 

[idleprocess]

Not only that, but focusing a single LuxV to give a tight beam is hard enough - I don't think anyone's found a solution for focusing *multiple* LuxV's (which you'll need to generate the same amount of light as the incandescent source you're wanting to replace). LED's are simply "not there yet" in terms of the amount of light they can generate (compared to incandescent light sources).

If one were going to make a "LED headlight," it would probably be a "compound beam" with a dozen+ emitters using a number of different optics to accomplish a variety of tasks rather than using a single reflector engineered to do all those tasks. I can see using at least 3 different optics/reflectors - long-throwing narrow-angle, medium angle for medium-distance fill, and some eliptical optics for close-up spill.

Needless to say, crafting this sort of beam would require a great deal of experimentation.

"3-4" Luxeon Vs aren't going to cut it since you're going to be lucky to get 120 real-world lumens out the front per LED; a typical 55-watt 12V halogen is pushing 1200+ lumens at the bulb; figure 35% loss with reflector & lens and that's 780 lumens. I'd throw at least 10 Luxeon Vs at this problem if you were up to fiddling with a variety of optics/reflectors for your beam... or 15+ Luxeon 3s.

I think I agree with your point about the color rendition of your typical "cool white" LED... maybe not a good idea when driving at high speeds.

 

[Handlobraesing]

If one were going to make a "LED headlight," it would probably be a "compound beam" with a dozen+ emitters using a number of different optics to accomplish a variety of tasks rather than using a single reflector engineered to do all those tasks. I can see using at least 3 different optics/reflectors - long-throwing narrow-angle, medium angle for medium-distance fill, and some eliptical optics for close-up spill.

Needless to say, crafting this sort of beam would require a great deal of experimentation.

"3-4" Luxeon Vs aren't going to cut it since you're going to be lucky to get 120 real-world lumens out the front per LED; a typical 55-watt 12V halogen is pushing 1200+ lumens at the bulb; figure 35% loss with reflector & lens and that's 780 lumens. I'd throw at least 10 Luxeon Vs at this problem if you were up to fiddling with a variety of optics/reflectors for your beam... or 15+ Luxeon 3s.

I think I agree with your point about the color rendition of your typical "cool white" LED... maybe not a good idea when driving at high speeds.

Your bike headlight is probably 55W or so and if its off-road only, it could even be 100W or more.

At this time, LED's do not come anywhere near matching the sheer output of such high power halogen lamps.

 

[Silver Surfer]

dang. you guys are good. i think you talked me out of the LED conversion. i will probably have to stick with stock 35 watt bulb. anything hotter draws too much current and will melt the stock plastic lens.

i appreciate all the good posts!:rock:

 

[prerogative]

Here's a stand-alone HID solution that may meet your needs: http://www.batteryspace.com/ProductImages/hid/thumb_twin_helmet_top.jpg
- There are benefits to the helmet mount (light where you look), so long as you have a good foundation of light on the bike as well.If you're looking for bike mount and willing to regulate (may not be required), 2-3 of these will do, and should be within your bikes output capabilities: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1393
- One could mix spot/flood reflectors, or control independent bulbs (switches) as desired.

Good luck.

 

[Silver Surfer]

if i do end up doing this, do the schematics using the 7812 regulator chip look OK? is one design better than the other? are there other better options available?

 

[idleprocess]

There's another "automotive" regulator chip that's better from what I remember ... higher voltage range, reverse-polarity protected, easily configured as a current supply, etc... I'll see if I can dig through my information - it would work dandy for regulating LED taillights...