LED replacement for bike light bulb

October 23, 2006 7:30 AM

Replacing a halogen bike light bulb with LED

I've got a cheap 10 Watt rechargeable halogen bike light that came with a heavy SLA battery pack. I've been thinking about building a nice light NiMH battery pack (6V) to make it a bit more portable this winter. The bulb is a standard MR16 6V 10W bulb. Out of interest I had a look online to see if you can get LED replacements for these and it turns out you can. Is there any reason I can't drop in on of these (the 3 watt luxeon mr-16 builb) and build my battery pack to 12V instead? Anyone care to take a guess at whether this would be brighter / dimmer than my current bulb? I've seen it claimed that a 2W LED puts out the same amount of light as a 20W halogen bulb, but I doubt it's that simple (although I'd be delighted to learn that it is!). Since the LED bulb draws ~300mA rather than ~2A I could make a lighter battery pack for the same runtime, even though I'd need double the voltage.

posted by primer_dimer to sports, hobbies, & recreation (8 comments total)

Is this just a battery pack or is it going to be continuously recharged by a generator on the wheels/pedals? If the latter, ensure that the generator can get up to 12 V.

Looking at the MR-16 I see an important note regarding your brightness question:

NOTE:
You may disappointed in the light output from LEDS if you a replacing halogen bulbs for general lighting.
In comparing the light output to halogen bulbs, the 12 White LED bulbs are comparable to about 7 Watts, 24 LED bulbs are comparable to about 15 Watts. The light output from our HO and LX bulbs are comparable to about 20 Watts of halogen.
The LED bulbs are for where you just need a little accent lighting or where power conservation is very important, such as battery powered applications.

And finally, I note that all these bulbs take AC voltage, not DC. Granted, you might be able to break open the case and remove the bridge rectifier, but it might be tricky.
posted by Xoder at 7:40 AM on October 23, 2006

You might already know this, but check out Peter White Cycles for some good info on lighting products. He says that halogen is a good choice for city riding, where there is plenty of ambient light and you want the light from your headlamp to 'cut through the clutter.' For unlit country roads he says that halogen bulbs are a better choice.
posted by fixedgear at 7:47 AM on October 23, 2006

Thanks for pointing out the brightness bit, Xoder. I'm more than happy with the amount of light put out by the current 10W halogen bulb, so a ~20W equivalent would be fine. It's going to be a battery pack only.

Under the MR16-WLX LUXEON LED BULBS bit it says:

Voltage Range: 10~15 Volts AC or DC

and

3 Watt: 45 or 100 Degree Beam pattern - 5500K CCT Cool White - 300ma current draw @ 12 VDC

Which made me think that DC wouldn't be a problem. Is it feasible that they could be designed to work with either AC or DC?
posted by primer_dimer at 7:51 AM on October 23, 2006

primer_dimer,

It certainly is feasible, and I simply stopped reading after "AC". Too early in the morning. My bad.
posted by Xoder at 7:54 AM on October 23, 2006

I've seen it claimed that a 2W LED puts out the same amount of light as a 20W halogen bulb, but I doubt it's that simple.

If you're talking raw lumens, candlepower, or whatever else unit of light output, then it's approximately true. Incandescent (halogen) bulbs are very inefficient: less than 10% of the energy they consumed is converted into visible light. The rest is given off as heat.

LEDs and HIDs are something like 30%-50% efficient. So for each watt of electricity consumed, LEDs and HIDs would put out many times more visible light than an incandescent bulb.
posted by randomstriker at 9:47 AM on October 23, 2006

Which made me think that DC wouldn't be a problem. Is it feasible that they could be designed to work with either AC or DC?

What this indicates is that the LED bulbs have a rectifier (LEDs being diodes, they are pretty much already rectifiers, actually :P), so that you can feed AC and have it become DC.

You can feed rectifiers with DC with very few problems. The rectifying diodes will drop the voltage slightly, and it will be slightly less efficient than it could be. You will also be stressing certain diodes in the rectifier constantly, and others not at all. In an extreme case this could cause a failure; however that is unlikely.
posted by Chuckles at 1:14 PM on October 23, 2006

primer_dimer, you sound very confident that you are looking at the right size bulb, so I hesitate to bug you about it, but.. Based on my window shopping experience, I think most bicycle headlight systems use smaller bulbs, presumably MR11 rather than MR16. Of course the site you link also has MR11 size LED bulbs, so..

The only other thing I can think of is beam angle. Get the narrowest beam you can find.
posted by Chuckles at 1:24 PM on October 23, 2006

A friend who builds his own bike lights said 5W LEDs are about as bright as 10W halogens, in practice. (I think he's referring to the Luxeon V). You're going to get more lumens per watt from an array of less powerful LEDs, but that array might somewhat harder to build a lamp with.

For rear lamps, red Dept of Transportation marker lights often use LEDs. Check out an auto or trucking supply store. Like most automobile lights, they come wired for 12V. So I would suggest going with the 12V battery you mention. It makes using truck lights pretty simple. You could use brake lights too for maximum visibility.

If your homebuilt LED lamps operate on less than 12V, you can always string some together in series. For instance, to make the voltages add up, an acquaintance threw in a 1W green ground effect LED instead of a resistor. You could see his bike across the lake. Just thinking of that nuclear glow makes me smile.

(Of course retroflective strips are important too, so cars see you when their lights shine at you.)
posted by blue grama at 9:07 PM on October 23, 2006