Hi,If I installed a 55w resistor in a circuit, will it half the light output of a 55w bulb?

 

How many ohms is the 55w resistor, what kind of circuit, and do you mean a 12V 55w bulb
like a headlight bulb?

Anyway, the short answer is no.

 

As Cristo stated it will not do that.

http://en.wikipedia.org/wiki/Resisto...llel_resistors

Here is a good read...

 

Longer answer, ... if you used a resistor with the same resistance that a 55W bulb has at 13.6 Volts (about 3.4 ohms)
and put in in series with the bulb, the voltage drop across the bulb would be 6.8 V, the current would be 1/2 what
you had before, and the power (voltage x current) would be about 1/4 of 55W or 13.75W.
But, ... the bulb will have a lower resistance when running at that lower voltage (cooler filament), so you'd have
a lower voltage drop across the bulb than the resistor, and you'd get even less output, and the light output per
watt (efficiency) of the bulb would drop quite a bit, so even less light output, and the color temperature would
drop as well, so you'd get a dim, orangy light from the bulb.

You'd get something closer to 1/2 the light output from the bulb in series with a resistor about 0.8 to 0.9 ohm.

 

What is your goal? If you install a resistor to halve the output, be careful where you mount it, because the resistor will get very hot (as hot as a light bulb).

If you want lower output, install a lower wattage and/or different type of bulb. Wattage is not linearly proportional to light output (lumens) and will depend on the type of bulb, so there isn't a simple formula to follow.

 

Maybe I could use a resistor from a daytime running light circuit. They have cages around them . I would like a set of 55w lights to run at half brightness, sometimes. How bright would 55w bulbs be run in series?

 

That would be a good start. If it's a pair of lights, connect them together in series on the same circuit. It's hard to say how bright it would be. Each bulb will receive half the power but that doesn't necessarily translate into half brightness. Different bulbs will respond differently to varying amounts of power.

 

looks like some bench testing is in order

 

In this case you'd have 1/4 the power (1/2 the voltage and 1/2 the current)
and considerably less than 1/4 the brightness since you'd be running
the bulbs at about 6.5-7 volts each depending on your alternator output.

 

so there is no good way of dimming the bulbs?

 

Well, as stated earlier, a 25 or 50 watt 0.85-ish ohm resistor in series with the bulb,
mounted in a way to dissapate heat, would probably work.
I also wonder, can the dealer activate DRL on your car?

Some cars have DRL capability, which can be turned on or off by the factory or dealer
depending on the target market or preference. Daylight Running Lights usually run at
slightly lower voltage and brightness than regular headlight mode.
Is the MINI one of these cars?
Here's a starting point: https://www.northamericanmotoring.co...on-a-mini.html

 

I tried a bench test,I found running the bulbs in series works well,the dimming is just about right, now I need to get creative with some relays and diodes.
(I'm not trying to run the headlights dimmer)

 

Have you considered lightly over spraying the bulbs with silver paint to reduce the light output? Alternatively you might be able to find a lower wattage bulb with the same base online.

 

Hi, I'm being kind of cagey , sorry about that. But I want to run a set of single filament 55watt bulbs at full power and at half power at will.

 

Sounds like an interesting project; if you figure this out please post the solution for those of us who are electron challenged.

 

got it figured out, now I need to buy some relays and such then do some bench testing

 

now I need to find male and female OEM Mini wiring connectors to make non intrusive T splices. I need connectors to splice into the driving light's harness and the fog lights.