DIY fluorescent tube lamp - effect of running "cold" leads through metal tubing

Thread Starter

seanspotatobusiness

Joined Sep 17, 2016
190
I have a vague plan to make a floorstanding fluorescent lamp (I don't want to use LEDs because I also want this light to be flicker free for my occasional video recording). The fluorescent tube will be inside a polycarbonate tube which will fit into recesses in the top and bottom parts of the lamp to protect it somewhat. The high frequency control gear will go in the bottom and I wanted to run the two "cold" wires through one of the steel tubes to the top of the lamp. My question revolves around a bullet point in the data sheet for one possible control gear https://www.tridonic.com/com/en/download/data_sheets/PCA_T8_ECO_lp_xitec_II_en.pdf - I might end up using a different control gear but I imagine the advice is still relevant. The bullet point says: "keep the distance of lamp leads from the metal work as large as possible" and is under an "RFI" heading which I suppose stands for radio frequency interference? Is passing the cold leads through the steel tubing liable to affect the function of the lamp? The hot leads would be very short and would not pass through the metal tubing. The leads would be twisted as suggested by the datasheet, although I don't know how many twists per unit length would be optimal. Can the RFI of the steel tubing be mitigated? The tubing would probably be 1600 mm long, 12.7 mm OD, 1.2 mm thick.

 

oz93666

Joined Sep 7, 2010
672
Hold everything!!

LEDs do not flicker ...unless they are fed flickering electricity , sometimes done in led lamps

Florescent lights always flicker at twice mains frequency ...

LEDs are by far the best choice ... warm white only ( normal white has too much eye damaging blue) ... you can have other colours ... infinitely dimable (florescent are not) .

Just use a normal powersupply with a good capacitor across the outlet and there will be no flicker

Also your design will not be comfortable on the eye , florescent tubes are OK out of eye line on the ceiling , but in close proximity it will be very troubling , this is also true for leds .. before you build this , just try having a florescent light where you plan to put this in the room ...you will soon change your mind .
 
Last edited:

Alec_t

Joined Sep 17, 2013
10,458
Florescent lights always flicker at twice mains frequency .
Old-school ones do, but modern ones with high-frequency ballasts don't. Unless that high frequency happened to be a harmonic of the video frame frequency it's unlikely that any strobe/flicker effect would be noticeable.
 

oz93666

Joined Sep 7, 2010
672
Old-school ones do, but modern ones with high-frequency ballasts don't. Unless that high frequency happened to be a harmonic of the video frame frequency it's unlikely that any strobe/flicker effect would be noticeable.
A search shows you're right .... I'm not sure if the ballast TS links to is flicker free , it doesn't say it is ....

But the main problem is the glaring light even if it is dimmed ... there's a reason for lamp shades , even on low wattage incandescent ..

Also the glass tube will be very prone to breaking , even if supported by 4 metal rods as shown , the glass will not tolerate the slightest bending or jarring .
 

DickCappels

Joined Aug 21, 2008
5,944
Alec_t has some good ideas. I think earthing the tubes is also a good idea for electrical safely, but make sure that all of your connections from the tubes to earth are at the same end of the tubes (likely the bottom end) so you don't turn the tubes into RF radiators for energy trying to couple to earth.

One thing that makes is difficult to answer your questions is what the cold lead has on it. The term "cold" might not mean anything having to do with RFI (yes -radio frequency interference).

For those who did not bother downloading the .pdf file:
RFI
• Connection to the lamps of the hot leads must
be kept as short as possible
• Mains leads should be kept apart from lamp leads
(ideally 5–10 cm distance)
• Do not run mains leads adjacent to the
electronic ballast
• Twist the lamp leads
• Keep the distance of lamp leads from the
metal work as large as possible
• Mains wiring to be twisted when through wiring
• Keep the mains leads inside the luminaire as short
as possible​
 

oz93666

Joined Sep 7, 2010
672
Poly-carbonate tube won't prevent breakage , just contain broken glass ..

The problem is poly carbonate is flexible so is steel to a much lesser extent , but glass is not , the slightest twisting or distorting of the upper block in relation to the lower block will cause all the stress to go on the glass .
 

Thread Starter

seanspotatobusiness

Joined Sep 17, 2016
190
I intended to make the base out of concrete so that should be pretty heavy. The connectors I intend to use for the tube ends will not be fixed in place so there will be less stress on the tube. I can probably suspend and support the tube from underneath with something spongey so there's even less stress.

The frequency of flickering will be between 44 and 120 kHz which I presume depends on the dimming but I don't know whether the higher frequency comes from the higher or lower dimming. It's definitely adequate for amateur filming.

I will earth all the support tubes. Thanks for everyone's advice!
 
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