DMM to test a bulb

[vhyper007]

G'day,
can anyone here tell me if a DMM can be used to test a bulb to see if it is still good. Me eyesight aint what it used to be and on some of these tiny bulbs it is hard to see if the filament has separated. Also, once a bulb has instaflashed it is muerte(dead) right?

Thanks, someone, for taking time to answer the dumbest Q of the day.

vhyper

 

[65535]

If the bulb shows resistance on the Ohm Setting then its still good, if it shows O.L. or something to the effect of nothing then it's shot, instaflash is dead unless you are using a flash tube, like in a camera flash.

 

[macforsale]

*

 

[vhyper007]

where do you place the leads on the bulb and where do you turn the dial on the dmm? and then what?

 

[Ookpik]

You set the DMM to the lowest resistance range. That's usually about 200 ohms maximum reading. You then connect the test leads to the contacts of the bulb. A PR2 bulb (for two D cells) that is rated for 0.5 A at 2.4 V measured 0.5 ohms on my meter. Since V/R=I, you would think the bulb would draw 4.8 amps of current. The explanation is that the resistance of the bulb filament increases when it gets hot and glows. The resistance of the bulb when it's producing light is about 4.8 ohms (V/A=R). If the bulb were bad, it would test OL or the maximum reading on the meter. If you set the meter to a higher resistance range, the bad bulb would still test OL (open circuit).

 

[mdocod]

I usually set it to test continuity first, if I get a BEEEEEEEP then I know there is at least a connection, if it still isn't working I might test ohms, but if it is BEEEEEEP then more than likely the problem is somewhere else in the flashlight (power isn't getting to the bulb)

 

[TORCH_BOY]

You can use the Diode tester, if it Beeps the globe is ok, if it doesn't the Globe is shot

 

[vhyper007]

ookpik, mdocod, andd torchboy,
thanks for your answers. i guess the formulas are v=volts a=amps r=resistance i=impedance. also, what is the diode tester, and what is the continuity tester.

type real slow. my electricalness rides the short bus. way toward the back, sadly. I can splice wires and do a drop in mod though, thank you very much. oh yeh, and change batteries without reversing polarity.

thanks much,
vhyper