Why don't Low Energy Bulbs show continuity with a multimeter?

Avoriaz

I normally check traditional filament light bulbs with a multimeter on the ohms resistance/continuity check.

This doesn't work with low energy bulbs.

Why is that?

I have googled and can't find an obvious answer.

Do they contain a diode or other device that will only pass AC above a certain voltage and won't pass the 1.5 volts DC that my multimeter produces?

Other than trying them in a socket, is there any other test I can do with a basic multimeter?

I know the socket test is obvious and easy. I am really just curious to know.

Thanks.

tonyh66

yes. essentially they are mini flourecent bulbs and the circuit has to build up enough current to pass through the gas within the tube

John_Gray

The Wikipedia article on the subject should contain more than enough information to baffle anyone!

Avoriaz

tonyh66 wrote: »

yes. essentially they are mini flourecent bulbs and the circuit has to build up enough current to pass through the gas within the tube

What about the starter or ballast device? I thought that might let enough of a small 1.5 volt DC current pass through to show on my multimeter.

Although, thinking about it, even if it did it would still not indicate whether the tube was functional.

Thanks for the replies. :beer:

skivenov

Not til it's charged, and your multimeter's continuity voltage will never charge it.

Fifer

Avoriaz wrote: »

What about the starter or ballast device? I thought that might let enough of a small 1.5 volt DC current pass through to show on my multimeter.

Although, thinking about it, even if it did it would still not indicate whether the tube was functional.

Thanks for the replies. :beer:

You cannot really check a fluorescent tube with a multimeter. The light is created by exciting gas ions on the tube - there is no continuity through the tube unless the gas is excited by a reasonably significant voltage. You should be able to measure across the complete light assembly (starter, tube and ballast) as the starter switch should be normally closed, but that doesn't tell you much about the tube other than that the cathode/filaments are intact and that the ballast isn't o/c.

Enterprise_1701C

No filament - no continuity.

paddyrg

Ballast isn't a coil any more, it is a circuit... The meter just doesn't kick out the power to drive it

mttylad

The meter gets nowhere near the gas or the ballast.

If you google images for "cfl lamp circuit" you get:
https://www.google.co.uk/search?q=cfl+lamp+circuit&hl=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=WdSrUKLSK5OzhAfZ6oGoDw&ved=0CB0QsAQ&biw=1032&bih=513

Which in many cases shows that there is a bridge rectifier in the circuit so diode test would be better.

You may also have a capacitor across the input.

The test is to put them in a known working lamp holder and turn it on, if it does not work its bust.

kwikbreaks

Khinie wrote: »

Blimey your thick!! :rotfl:

An interesting observation - especially as it comes from someone who opened a 4 month old thread purely to make it.

Oblivion

Khinie wrote: »

Blimey your thick!! :rotfl:

I expect he can spell you're correctly though.