# Light Resistance

when you buy a light bulb, do they tell you the total resistance the light bulb creates?

i'm going to be using light bulbs for a physics project, and i was wondering if i am going to have to solve for the resistance provided by the light bulb or if it's going to be given to me

The resistance of an incandescent light bulb fillament at operating temperature is about 100 times greater than it is at room temperature.

Also, the fillament has some inductance because it is a very tight spiral within a spiral (visible only under a microscope). So the total inpedence, is a combination of inductance and resistance. I think the inductance is quite small compared to the resistance.

The light bulb's package will give a little more info than the label on the end of the bulb.

You can get more info by going to the manufacturer's web site and looking up the specific part number. Note that the voltage you get from the power company may be significantly different from what the spec sheet calls for. I live close to a substation and get 125 vac; customers near the end of the line might get 110 vac. Try shopping at an electronic surplus store for a cheap variac transformer so you can test light bulbs at different voltages.

If you are planning to compare incandescent bulbs to fluorescent bulbs, you need to know that the electricity goes thru a ballast which converts to high frequency and high voltage. You cannot directly measure the resistance. Fluorescent bulbs are rated according to the power they consume and the equivalent power of the incandescent bulb they are meant to replace.

The difference is that fluorescent bulbs emit a larger share of the power as light before it is absorbed and becomes heat. In an adiabatic chamber, you will measure the same amount of heat from a 26 watt fluorescent as from a 26 watt incandescent, but the fluorescent provides about four times as much light.

If your home is heated by electric convection (not a heat pump) then you can get as much light as you want for free (in winter) as long as it is less than what the electric heater would be using.

Muse- The Making of "Guiding Light" (The Resistance DVD)

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