Science Buddies: "Ask an Expert"

I have completed the project "The future of LEDs is so bright, I have to wear shades" . I would like to compare my findings about incandescents and LEDs to flourescents. Can this be done with the test setup I have already made? If so, how?

Hi and welcome to the forums:

Due to the fact that fluorescent bulbs require a ballast (because of their high start-up currents), I don't think you can use any of your electrical power measuring circuits. You could use a "Kill-A-Watt" and a low power fluorescent (CF) bulb for this purpose, however. You're "lumen" measuring apparatus could possible be used to measure the light output of the CF bulb. HTH.

Keith

The wattage ratings on Compact Flourescent bulbs are fairly accurate as long as the voltage they are plugged into is 120 VAC because they have an integral ballast. This means that you could use a digital volt meter to measure the AC RMS voltage to determine the adjustment. CAUTION: There is a shock hazard when measuring voltage and you should have someone trained in doing this safely assist you.

For example, if you measured the voltage at 115 VAC RMS, the would be 96% of the nominal design voltage and the current would also be reduced to 96% which means the wattage would be 92% of the nominal rating. If you measured the voltage at 125%, that would be 104% of nominal and the current would also be 104% of nominal so the wattage would be 108.5% of the nominal rating.

Ratings on flourecent bulbs designed for use with separate ballasts aren't as accurate because of large variations in the ballasts.

The same technique can be used for Tungsten bulbs; however, you should look at the voltage ratings on the top of the bulb to determine what their design voltage is for their wattage rating.

The "Kill-a-Watt" device is certainly a safer way to make the power measurements and I would recommend using it if you don't have access to someone trained in assisting you.