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Technology / Cheap Chinese compact fluorescent lamps

« on: 06/02/2009 13:49:27 »

I can't measure AC current. I have two DT838 digital multimeters that measure only DC. I had an idea to connect the light with a diode (or 4 diodes for full wave rectification) in series and then measure the current (and I will probably do that just for fun), but that would probably affect accuracy. Or maybe I could connect it with and incandescent light in series and then measure voltage on it's ends, or something like that??

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Technology / Cheap Chinese compact fluorescent lamps

« on: 04/02/2009 13:20:53 »

They cost two or three times less then a good CFL, and it seems that there are only daylight (6500K) models. Their power ranges from 20 to 50 watts, but their light output is low. They are as bright as incandescent bulb of the same power.

I was just wondering - how can you make a fluorescent lamp so badly. If you had too little mercury in it, it would glow red (neon and other gasses), if the phosphorus layer was too thin it would be bluish or violet. Light output per watt of all fluorescent lights should be roughly the same, right? Then I opened few of them, and few good CFLs and I noticed that good ones have transistors rated for much higher power than Chinese ones. Chinese lamps are also a lot cooler then normal CFLs, the one I now have in my desk lamp is rated at 36W, but is is as warm as 36W 4ft fluorescent tube, only slightly warmer than room temperature. Even if they had terribly inefficient phosphorus that absorbs more UV than it converts it should be a lot warmer, right? Electronic ballast should be warm too if it really gives 36 watts, but it's not warm at all.

My conclusion is that these CFLs use only about 10-15W, and that the Chinese only stamp higher numbers to trick people into thinking that their lamps are good. What do you think about this?

The reason that I'm making all this fuss is that I could really use about dozen of cheap CFLs even if they are dim (desk lamps, closets...), but if they consume the amount of power that is stamped on them, then it has no point. I have no easy way of measuring the power, I have only two multimeters, but none of them can measure AC current (and then there's power factor...).

Btw, I'm from Serbia, and I think that these crappy CFLs are only exported into crappy countries like mine, I don't think you can buy them in any normal country.

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Technology / Fluorescents in cold weather

« on: 11/12/2008 14:36:12 »

I know that fluorescent lights are usually not good when it gets too cold. They can't glow as bright as when they are at room temperature. But what happens with power consumption? They are dimmer because the density of mercury atoms drops, and there are less collisions with electrons. But the number of electrons should be the same, so the power consumption should also be the same. Am I right?

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Technology / What is the pressure in fluorescent light

« on: 11/12/2008 14:21:09 »

...and how would efficiency be affected if it was different? I've read on wikipedia that the pressure is only 0.3% of atmospheric pressure, is this true, wouldn't that crush the glass?