Overdriving fluorescents

[jtr1962]

I found this article describing how it is possible to parallel the outputs on a multi-tube electronic ballast to drive one tube at increased output. A good candidate for doing this with is Home Depot's very low cost shoplight (SKU # 140904). Using two shoplights it is possible to use each ballast to drive a single tube at about 1.7 times the normal power level. Of course, you have one empty fixture left over, but that can come in handy. Although I put everything back to stock configuration after testing, I did try it and it really does work. I can get ~5000+ lumens out of one of my F32T8 full-spectrum tubes (rated output at 32 watts is 2950 lumens). Input power per tube is about 55 watts, and the tube does get somewhat hotter than normal but still not too hot to touch. This is a great way to save money on tubes if you need a very bright light and don't care about getting rated life. For 110 watts power input you get a shoplight putting out ~10,000 lumens. Tube life is reduced, but those who made this mod say they have had tubes burning 12-14 hours per day for almost a year with no burned out tubes yet. I would guess life might be cut by half or even two-thirds, but since my full-spectrum tubes are rated for 34,000 hours, they should still last at least 10,000 hours. I've heard mild overdriving(up to 15%) produces no reduction in tube life at all.

[Brock]

Speaking of this, it seems as though some "shop lights" drive them harder then others. I have found that the Home Depot zero start or cold start drive them about 30% brighter then the cheap ones, and they start VERY fast. I have had one of each and the dimmer one tends to burn through tubes at about twice the rate of the brighter ones.

[jtr1962]

Which two shoplights are you comparing? I only have this particular type of shoplight (5 units total so far) so it's hard to do any comparisons, but the tubes start instantly and seem to burn very brightly even without the overdrive modification. Based on the measured input power (~67W), and assuming a 90% ballast efficiency (typical for electronic ballasts) about 30W is delivered to each tube. The 32W lumen rating is on a magnetic ballast. Tubes are more efficient on high-frequency electronic ballasts by about 10 to 15% depending upon frequency, so the tubes should be putting out the same amount of light as they would driven to 33W to 35W on a magnetic ballast, or about 3100 lumens each. Overdriving as I described increases output by some 65%, so the tubes would put out maybe 5100 lumens each.

BTW, the dimmer shoplight you mentioned is probably driving with a non-optimum waveform, and that is what is making the tubes burn out faster (unless it's being started more often than the other one). Lights of America shoplights were particularly bad in this regard. Frequently, tubes would burn out as fast as incandescents, or the ballast would go completely. Home Depot's ultra cheap shoplight ($7.95) seems to be cheap in price only. As I said in another thread, I'm amazed they can make money on these.

[Brock]

I am not sure what the cheap ones I have are. They are older and the newer ones specifically said they were "0" start, as in being used in unheated shops and garages. I swapped the ones out in my dad’s garage and they do indeed start to about -10F (-20C), below that and you have to touch the end of the lamps. The ones I took out are the old ones I am using; they wouldn't start below 20F (-6C).