I currently own a 60's/70's vintage light for my bike. I have it attached to my Trek 820 series 26" mountain bike at the moment.

The light worked perfectly fine until one day when I broke the bulb inside. The bulb was marked on the side being 2.5v, even though I know for a fact that the generator on the back wheel puts out about 6 volts.

I have tried several bulbs from Radioshack, and none work or are as bright as the previous bulb inside my Reynold's light. Is there anyplace on the web where I can Find such a replacement bulb? Are there any stores that mint have what I'm looking for? I tried Home Depot also, no luck there...

Thanks in advance!

  • 1
    More information about the kind of light, if you have it, might help. Commented Aug 30, 2011 at 18:59
  • 1
    Maybe posting a picture of the light would help.
    – Kibbee
    Commented Aug 30, 2011 at 19:16
  • Typically, the lamp would have been a halogen one. I used to have a spare that might have worked, but tossed it about a year ago. Commented Aug 30, 2011 at 19:21
  • Would help to know if it's threaded or bayonet base. Commented Aug 30, 2011 at 19:22
  • 1
    You really need to give us more to work with. I suggest multiple pictures. The light; any identifying features of the light; the spot the bulb fits into; and the bulb, especially the bit of the bulb that fits into the light.
    – freiheit
    Commented Aug 30, 2011 at 20:34

3 Answers 3


This is nothing more than a standard dynamo front bulb - 6V 2.4W is what you really need (the rear is 6V 0.6W). Most Northern European bike shops carry screw-in Halogen versions of them for 'Union' brand headlamps of your vintage:

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If you are not running the rear light from the dynamo then you need a 6V 3.0W bulb in the front. (2.4W + 0.6W = 3.0W).

The problem with the simple two-bulbs-in-parallel circuit is that if you remove one light (e.g. a broken wire) then too much current goes through the remaining bulb and it blows.

Think about it, go to the bike shop when you have a problem with the bike, not the electronics store or the car-parts store or the aromatherapy store. The staff in the bike shop do know a thing or two, they have heard of bicycles running dynamos and, even if they don't have spare dynamo bulbs to hand, they do have a supplier that they can get them from for you in a reasonable period of time for a price that will not cover their time dealing with your enquiry.

I suggest you visit the LBS first, they may only be able to get you the 2.4W version, if they can get you the 3.0W version then get it and a flashing light for the back. In that way you will have a rear light that works when you stop, more light up front and less likelihood of blowing the bulb (because there is no rear bulb to blow).

Alternatively, get a new front headlamp unit for the dynamo, these may be special order from the bike shop, however, such a unit will have niceties such as a better reflector and lighter construction.


I would take the light into your local auto parts store and have them peruse their catalogs of specialty bulbs for something to fit this. Auto parts catalogs often have specs that will help understand the type of bulb base options, wattage/power and voltage requirements.

Actually, I found this site in about 30 seconds that should help out.



I strongly suggest you have a look at the "REFLECTOLITE" range of lighting supplies. They have bulbs for every type of light - including dynamo lighting. You'll be wasting your time and money going to motor factors. Cycle shops may be able to help but Reflectolite are the best bet - give them a try, you won't regret it.

  • This reads a lot like an ad. Are you associated with this company? Commented Nov 14, 2017 at 11:03
  • Welcome to Bicycles SE. Are you affiliated with the site you mention? If you are, you must disclose that affiliation within your answer. bicycles.stackexchange.com/help/behavior
    – jimchristie
    Commented Nov 14, 2017 at 13:15

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