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Dimming a US bulb with 1N4007 for use in 220v 50hz

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#1

Hi there,

I’m working on making a US Incandescent light bulb compatible with 220v 50hz power so it can be used in China. The tungsten filament looks great and I’d like to keep the bulb (I don’t want to source a new bulb locally). Some google search indicates a solution simply by connecting a silicon diode (e.g. 1N4007) in series with the bulb to permanently dim it. Someone also pointed out that this would cause flicker problems. Anyone have any comments on the feasibility of this? Will the flicker be noticable? More importantly, is this procedure safe? Of course the “artistic” bulb will not be of heavy duty daily use, but are there any foreseeable problems?

#2

I have a lamp that uses the same dimming technique. The flicker is somewhat noticeable, but would probably be more apparent at 50hz. You didn’t state the wattage, that diode may be sufficient (maybe two in parallel if you want to go crazy and throw 50 cents at the problem). Although, I would guess that 220V “artistic” bulbs or dimming modules are readily available as well.

#3

Hi ji.Shi,

Welcome to the Tech Forum.

I see two potential problems with your plan. First is that of the instantaneous power issue. If you use a diode with 220Vac, the average power would be in the same neighborhood as 110Vac since it only conducts half the time, but the peak current would be twice as high and I’m not sure how well the tungsten filament can handle that. I would think it would stress it more than than running full wave at 120Vac.

Second, I believe there would be a greater issue of tungsten migration running DC through it. Tungsten will tend to migrate to one side of the filament with DC, whereas with AC, the migration averages out to zero because it pulls it equally in both directions. This causes thinning of the filament and premature failure.

#4

Hi David,

Thank you for your comments and for taking the time to point out the potential problems.
Seems the bulb itself is the problem. What if I source a 220v bulb locally and replace the 110v bulb. Based on google, the E27 and E26 socket should be compatible with each other. Will this work? Do you forsee any issue in other parts of the system, the cord, the on/off switch? Thanks!
(btw, the original bulb is 60W)

#5

Hi Matt,

Thank you. That’s a good point and makes perfect sense. I guess I’ll just find a 220v bulb instead. Will this make the whole thing work by simply replcing the 100v bulb with a 220v one?

#6

That’s interesting, never heard about tungsten migration. Are regular DC incandescent filaments not made from tungsten?

#7

I would think so, if it is a basic lamp with electromechanical switch
If the following is true:
-The 220V bulb fit into the fixture
-The plug will fit into the receptacle
I have seen a lot of those universal type receptacles in China

#8

Agree, best to use one designed for 220Vac.

This phenomenon is referred to as “notching”. Apparently it is more of an issue with thinner filaments, as they can’t afford to lose as much material, but as a rule, DC will shorten the life of any filament bulb to various degrees. Apparently, rhenium tungsten is sometimes used in DC bulbs to reduce the effect.
Here are a couple of sources which make mention of this:

#9

Hi David,

Thank you! What you posted is very educational! Much appreciated!!