I'm trying to rearrange the shop lights in my basement, they all use vintage 40 watt T12 lamps. I noticed some are noticably brighter than others, so I brought out my kill-a-watt. Here's what I found:

1) Decent quality fixtures with magnetic ballasts, rated 40 watt T12 only: 86 watts, bright
2) Chintzy residential grade fixture from the 80s, magnetic ballest, rated 40 watt T12 only: one is 86 watts and is bright, one is 56 watts and is dim
3) Decent quality electronic ballasts, rated for "4 foot T8 or T12", 56 watts, bright
4) Chintzy residential fixture with electronic ballast, rated "25,32, or 40 watt T8 or T12": draws 56 watts, dim. I opened this one up and ballast is very small and by "Keystone".

What's going on? Shouldn't these all be drawing more than 80 watts?

What's going on here is Ballast Factor.
Ballast Factor is how much a ballast drives a lamp of the tube's rated wattage.
Normal Ballast Factor is actually .87 to .88, so a 40 Watt lamp will only get 35 Watts.
High Ballast Factor is usually around 1.1, so you'll get 44 Watts from a 40 Watt lamp.
Low Ballast Factor is usually about .4 to .7, so the tubes will be dim.
You also have to watch out for Power Factor, so measure VA, not just Watts.
What's even more confusing is why Low Ballast Factor ballasts even exist.
I found that my Litemaster lamp drives F15T8 lamps at full power.

So here are the VA ratings:

Decent Quality Electronic Ballasts and Decent Quality Magnetic Ballasts: 80
Chintzy Magnetic Ballests: 56 and 76. These are identical fixtures so is the first ballast defective?
Chintzy Electronic Ballast: 46. Is this actually a 25 watt ballast that supposedly accepts full wattage tubes?

Seems like a decent quality fluorescent shoplight costs as much as an LED one, so maybe it's time to move that direction.

So here are the VA ratings:

Decent Quality Electronic Ballasts and Decent Quality Magnetic Ballasts: 80
Chintzy Magnetic Ballests: 56 and 76. These are identical fixtures so is the first ballast defective?
Chintzy Electronic Ballast: 46. Is this actually a 25 watt ballast that supposedly accepts full wattage tubes?

Seems like a decent quality fluorescent shoplight costs as much as an LED one, so maybe it's time to move that direction.

Are the ballasts high power factor?
It looks like your decent one is.

Don't go over to LEDs no don't do it! Is chintzy a US manufacturer? I think the different VA ratings might be due to some fittings having defective PF capacitors. Also make sure that its not down to variations in mains voltage

Don't go over to LEDs no don't do it! Is chintzy a US manufacturer? I think the different VA ratings might be due to some fittings having defective PF capacitors. Also make sure that its not down to variations in mains voltage

Chintzy is not a brand, it is a way of describing Cheapo items that have bad quality, and barely works.

Seems like a decent quality fluorescent shoplight costs as much as an LED one, so maybe it's time to move that direction.

If ya gonna decide to go LEDs. Go with name brands from physical stores. Check reviews on them too. Go with one that has good reviews and good warranty policies.

Don't buy generic from eBay or Amazon. No don't do it!

If keeping with classic fluorescent. Ask around here in forums or gallery of LG. Someone might have a good shop light to spare to sell or trade.

Quote from: mdcastle on July 28, 2016, 10:30:05 AM

Seems like a decent quality fluorescent shoplight costs as much as an LED one, so maybe it's time to move that direction.

If ya gonna decide to go LEDs. Go with name brands from physical stores. Check reviews on them too. Go with one that has good reviews and good warranty policies.

Don't buy generic from eBay or Amazon. No don't do it!

If keeping with classic fluorescent. Ask around here in forums or gallery of LG. Someone might have a good shop light to spare to sell or trade.

My 2 F40T12 shoplight needs a new home, but I don't want to sell it right now.

Is there a ballast that will drive both T8 and T12 lamps to their full output?

Is there a ballast that will drive both T8 and T12 lamps to their full output?

The best you can do is High Ballast Factor ballasts, which overdrive the tube a little bit.

Is there a ballast that will drive both T8 and T12 lamps to their full output?

No.  F40T12 and F32T8 lamps have totally different voltage and current requirements.  They will light if you mix them up, but they won't last long.

Some of my shop lights are rated for both T8 and T12...

The F32T8 is rated for 0.25A, the F40T12 is 0.43A.
So if the ballast feeds 0.25A, it will feed the full 32W into the F32T8, but barely 24W into the F40T12, so ballast factor of barely 0.6. If the ballast correctly heats the filaments, the lamp life will be fine with both, so may operate both lamp types.
With electronic is feasible even that the ballast identifies the lamp (the F32 has arc voltage drop of about 140V, the F40 around 110V) and so sets the proper current accordingly, so it operates both lamp types at full rated power. But then you should never mix the lamp types on one ballast (installing one F32 and one F40 on a two lamp ballast of this type), because the identification may get confused and so select the wrong current setting (e.g. 0.43A) and so destroy one of the lamps (the F32) and even get overloaded by itself (0.43A fed into F40 and F32 means total power of about 95W, while the ballast front end could be designed just for 80W load).


The low ballast factor has a good use: In many cases you need quite well diffused light for your work, so a long, thick fluorescent is a good light source for that. Plus sometimes you need two tubes running out of phase to suppress the stroboscopic effect.
But because it is placed close above the desk, running it at full power would mean way too bright. So using long tubes and powering them at level just needed for the task is the best combination - hence the "shoplite" ballasts powering the F40 at about 25W or so.
Of course, technically correct would be to design a special lower power tube for that use. But because the so widely used F40 mass production made these lamps so cheap, compare to that the special lamp would be just too expensive with only minor performance gain (efficacy in few percents,...), so it was just way more convenient and easier to operate the common F40 at the a reduced power, so the illumination level was about right.

What about this one? Will do both T8 and T12. Is this basically a T8 ballast that underdrives T12 lamps?
http://www.pillarsurplus.com/Pony-Solid-State-Electronic-Flourescent-Ballast-p/l002254.htm
http://www.warehouse-lighting.com/Shared/Product%20Downloads/Fulham/NPY-120-240-T8.pdf
Has a .8 ballast factor when used with T12 lamps. I eventually want to convert to T8 lamps but I have a lot of T12 lamps to use of first and some T12 ballasts that don't seem to work too well.

It could be. But as I wrote, better do not mix the lamp types.