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Thread: Magic Light?

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    Magic Light?

    Here's a real-life poser for the electrically-minded. I bought one of those little plug-in night lights, with a 5W fluorescent U tube inside. If I plug it into a power point, switch on the power point, then switch on the light switch, it comes on... nothing unusual about that. If I switch it off with its own light switch, it goes off... as expected. BUT if I switch it off at the powerpoint switch, it retains a faint glow at one end of the U tube. This seems to persist for, well... ever.

    What's the explanation?

    Alan

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    Re: Magic Light?

    Hi Alan, I haven't forgotten this and have been pondering over it for a bit...so here is my starter for 10.

    As it is a fluorescent light , there normally requires a starter.When the switch is turned on, on a normal strip light the starter's contacts heat up and open, interrupting the flow of current and the tube lights.

    Similarly, these little 5 watt lights need an amount of current to heat it up and get a starter to cause the current to flow. These night lights do not have a starter like traditional strip lights so they have to have another method of getting a current flow. They therefore use a method called "hot at all times" and there is a small short across the switch. By connecting a jumper wire from the "hot at all times" wire to the Earth, the light "powered" when the switch is off. However, when you switch the lamp off , you break the "hot at all times" contact and therefore the link to Earth and the light goes off.

    I think I have it but I don't have the electrical engineers terminology to explain it posh like <img src=/S/sad.gif border=0 alt=sad width=15 height=15>
    Jerry

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    Re: Magic Light?

    Interesting Jezza. I didn't know about the starter issue, but it makes sense that such a small/ cheap unit wouldn't have one. I still can't see how, if I've broken the active by turning off the powerpoint switch, that there could be any juice flowing anywhere... unless there's some sort of internal capacitor storage or similar.

    Alan

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    Re: Magic Light?

    I would guess there is some kind of phosphorescence going on - I can't believe the glow would remain forever.

    If it does - I take out a patent on it quick <img src=/S/laugh.gif border=0 alt=laugh width=15 height=15>

    (Point of interest: Wireless energy promise powers up, but I still would feel safe standing between transmitter and receiver with the number of fillings I've got.)

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    Re: Magic Light?

    Well I guess it is appropriate that the MBP would help us find a partial solution to using less electricity - turn off the electricity and generate some light ! I think I want some of these devices.
    Approximately how long does the glow last ? Your "for .. .ever" description is probably poetic, or is it ? Is it still on an hour after you switch off the power point ?
    Paul

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    Re: Magic Light?

    You and Leif are right, of course. "for... ever" equates roughly to " <img src=/w3timages/censored.gif alt=censored border=0> - it's cold. Nope <img src=/S/nope.gif border=0 alt=nope width=15 height=15> - taking too long. Outa here! <img src=/S/flee.gif border=0 alt=flee width=25 height=25>"
    I'll do a proper timed test when I'm feeling less whimpy.

    Alan

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    Re: Magic Light?

    <P ID="edit" class=small>(Edited by AlanMiller on 11-Jun-07 02:17. Update - Now 4.5 hours of "free" glow!)</P>Just to qualify - "forever" is now 2+ hours... and counting. I'll check as the night progresses.

    Alan

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    Re: Magic Light?

    Hi Alan. Does this page shed some light on your question?
    <font color=blue><font face="Script MT Bold"><big>Rob</big></font face=script></font color=blue>

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    Re: Magic Light?

    Your recent data suggests that you may really have a puzzle on your hands if your lamp is a basic, simple, fluorescent night light.

    Many fluorescent lights exhibit delayed photoluminescence, which means that the phosphors in the tube emit light AFTER having been illuminated by higher energy photons. In the case of fluorescent lamps the pumping light is predominately UV created by the gaseous discharge. That having been said, I am not aware of any phosphors whose decay times are measured in hours.

    I am also not aware of any basic lamps, in any technology, that emit light when the power is removed as your lamp seems prone to do.

    Ergo, the only kind of device I know of that fits your data thus far is a combination night light/power failure light. The night light is fluorescent. The power failure light is an LED (light emitting diode) powered by a small rechargeable battery. As long as the device is plugged into a hot socket the battery is charging, independent of the setting of the device switch. That switch simply turns the fluorescent lamp ON/OFF. But, cut the power to the receptacle as you have done and the circuitry senses power failure and turns on the LED. A typical time for the LED to stay illuminated is about 3 hrs.

    SO my best guess with your current data is that you have a night light/power failure light. Time is the issue <img src=/S/time.gif border=0 alt=time width=32 height=48>

    Paul

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