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LED replacements for prefocus headlamps - looking for suggestions

Stude Light

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For my 1939 LaSalle, 6 volt, positive ground. Currently using a 2330 bulb.


There is plenty of discussion around LED bulbs but I just haven't found a post discussing success with prefocus lamps. Has anyone had success using LED bulbs in a prefocus headlight design.  I'm looking at just switching to a halogen prefocused bulb but wondered about how well and LED would work. It seems that the exact position of the filament is critical and I'm doubting an LED could be used to have both low and hi beam usage. If you've had good experience, would you have a suggestion on a supplier?


Also, my dash lamps are not very bright - how about an LED replacement bulb for those? I think it's a GE55 bulb currently.

Thanks for any insight.


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I have a 1923 Cadillac (6V, positive ground) with #1133, single filament, pre-focused bulbs.



I have ordered a set of LED replacements from LEDLight.com in Arizona.





The focal point dimensions appear to be a good match for the 1133 bulbs, so I decided to try them.

I will post an update when I get the bulbs.


I haven't done any research on dash or other lights, but LED substitutes are available for most base and bulb styles.


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Headlamps, prefocused (with the ring so you don't have to adjust focus when you change a bulb) and manual focus (bayonet sockets that you focus mechanically) both are focused lamps.


The reflector is designed around a small point of light. In many old designs that had v-shaped filaments the "hot spot" is effectively a sphere. In newer designs, usually the filament is straight and there is a tiny cylindrical shaped light source.


Usually the cylinder of light is placed front to rear in European-influenced designs, and side to side in American influenced designs.


In September 2020 as I am writing this, an LED does not yet simply hang out in space like a filament and throw light in all directions. The LED itself throws light out the front (as of September 2020) and requires a heatsink on the back. For this reason it is currently impossible to simulate a filament. Lens and reflector systems have to be designed around the LEDs to work properly.


On high beam, moving the spot anywhere other than the focal point defocuses the beam. You can get bright, but probably not shine very far. On low beam, a second filament is off center of the focal point and is intentionally defocused, but if the light source is not in the expected place, it still probably wont hit the road in the expected pattern.


If you look at the construction of an LED bulb, you will see the problem. In recent times I have seen some LED replacements that have LED light sources sunk down deep in slots in the heatsink fins. This gets the light a lot closer to where it needs to be, and has to be a huge improvement over the ones that came before. It still isn't really close enough. A bulb is likely to outperform it for visibility, although the LED probably looks brighter (and whiter too) to oncoming traffic.


If any of you guys try them, please report back. LEDs will be a really great thing for our antiques if they ever get LED replacements really working good. The light output is so high and the current draw is so low.


EDIT: What I wrote above only applies to headlights and other focused lights, like driving lights. LEDs should (and do) work great in tail lights, brake lights, signals, etc.


EDIT 2: Stude Light, Yes you can brighten up dashlights with LEDs and several members here have done it. It works fine.


Dash lights back in the day were often run dim on purpose, so that your eyes would adjust to the dark and get the most out of the (probably lousy) headlights. If the car happens to have only a switch for the dashlights and does not have a dimmer, It is almost a certainty that the dashlights would have been engineered dim.


LEDs draw less current and make less heat at the same brightness level, so there is really nothing to stop you from sticking in some LEDs that have higher light output if bright is what you want. You probably won't overheat anything.


Edited by Bloo (see edit history)
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  • 2 weeks later...
On 9/21/2020 at 12:37 PM, Bloo said:

You can get bright, but probably not shine very far.

That is my experience. My 1939 Plymouth has 2330 pre-focus bulbs. I tried LEDs. They were very bright, but not useful as they did not penetrate the darkness very far. I replaced them with halogen 2330 bulbs. Worked much better, though I changed to an alternator due to the current draw.



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