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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
This is a simple idea, just take your normal fluorescent tube, make electrodes on the outside of its glass surface and connect to HF HV supply. But why? Because I believe the lamp life would be greatly increased this way as there are no electrodes to burn out.
The only problem I noticed is that the electrodes get quite hot, but I guess this can be improved(?)
Has there been anything like this done before?
I know of the electrodeless induction lamp but I haven't been able to find any info on how its driver circuits actually works.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
This technology is common in modern LCD backlights. They are called EEFL - External Electrode Fluorescent Lamp, a google search on that might give you more info.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
I suspect that the light output that you're getting there isn't as high as with proper heated electrodes. Something to do with thermionic emission I think? Glass is quite a lossy RF dielectric so that might account for the heating you observed beneath the electrode strips. Ozone generation is also likely!
But, yes there are cold cathode fluorescent lamps. I even once saw a demo of a lamp that ionised the filler gas with an intense alternating _magnetic_ field supplied by a thick coil of copper tube around the outside of the glass bulb! The advantage apparently being extended lamp life! I wonder if it ever passed EMC testing!
Registered Member #1999
Joined: Thu Feb 26 2009, 07:58AM
Location: Salem, Oregon
Posts: 4
I've been using a similiar approach on plasma tubes. The problem I was having with a direct connection was that once the plasma streamer had established an orderly flow there was no movement of the streamer in the tube, just a straight line. Using the coupling that you're speaking of on one side of the tube and a direct connection on the other side created a helix type streamer that was a bit chaotic, and variable by changing the frequency and pulse width, exactly what I was looking for.
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"Electrodeless" capacitive coupling fluorescent lamp?
