I think someone on the other thread listed the exact steps to overdriving the walmart units in another very recent thread. If I am imagining things I can write down my exact steps.

I have bought 12 of them now (for creating 6 fixtures) and every ballast has worked fine, although look for a box that hasn't been beaten up because they're packing isn't the best (chipped reflectors are possible).

Today I bought an 8 bulb T5-54W unit and it puts out about 30% more light, but it all appears to be in the reflector. In other words when I put mylar on the Walmart reflectors to cover the white paint I gain about 25% more light. The more expensive walmart reflectors ($15) with the silver finish are MUCH worse. They lose tons of light compared to even the cheap white ones, so stick with the $7.92 cheapos. Beware though that some walmarts will sell these for more, as they appear free to do so.

Jason

i remember reading once that contrary to popular belief, plants do not actually need a "rest period" of darkness

Some do, some don't. But the question shouldn't just be "is it bad for them", but "is it better for them". Running a few hundred watts of light for little or no gain is one way to heat your basement but not the way I'd choose :) I grow cacti and they don't grow at all in 24hr light, not the result you'd expect! Eventually they would die, but I've never pushed it that far.

Today I bought an 8 bulb T5-54W unit and it puts out about 30% more light

More than what? A 54W T5 definitely puts out more light than any T8 of the same size, but quite likely less than many overdriven 4' T8 or T12 tubes. And how are you measuring the light? It is really quite difficult to measure the total light output from a fluorescent fixture, or even the total light falling on a given area.

The 54W T5 light fixture put out *25% than T8 bulbs overdriven to 54W via two Walmart ballasts. As I attempted to say, the light is nearly identical once you put a superior refector behind a walmart ballast mounted bulb. The silver reflector is exceptionally bad, clearly worse (even to the naked eye) than the white reflector but the proof is the in the measurements.

In the case of white vs. silver, the scattering is the same so it is an entirely fair comparison. In the case of the T5-HO vs the T8 overdriven, the comparison isn't quite as accurate due to the different reflector design, but nonetheless I stand by my claim that overdrivin T8 bulbs in the walmart fixture are very close to as bright as the 54T5 bulbs. However, the T5 fixtures are just very convienent so I thought I'd pick one up. It was nice not to have to rewire the ballast before firing it up.

* I know I said 30% before but in reality it was 1/3rd of a stop which I forget is about 26% more light. It's a common misconception that 1/3rd of a stop is 33% more light.

I'm using a couple of the silver/stainless finish fixtures and I am liking them ... but now I have an urge to paint the reflector surface with some white spray paint.

Sure, triphosphor T5 and T8 on high frequency electronic ballasts should produce roughly the same light output when operated at the same power. In practice a 2x overdriven 32W T8 is likely to be running a little more than 54W and quite possibly producing more light than the 54W T5.

Of course you don't know just what power your overdriven system is drawing unless you apply a meter externally. Trying to calculate it only gives a very approximate value. Ballasts are current regulators, not voltage or power regulators, so 2x overdriving passes about double the current through the tube. This produces less than double the power usage because the tube gets hotter, more ionised, and the voltage across it drops. The ballast may also allow a somewhat different current to flow when the tube voltage is way off spec, as with an overdriven setup, so you really have no chance of calculating the power. Saying a 32W T8 (probably closer to 28W on a typical electronic ballast) overdrives to 54W is only a very rough approximation.

And it simply isn't meaningful to compare fitting efficiency in the way you describe. The eye is completely useless, so forget what you see. A light meter only measures the intensity at one point. Maybe the silver reflector is focusing the light less so it is spread over a wider area. Or maybe it is focusing the light more but not quite where you are measuring. Plus your meter is only accurate to plus or minus 10% at best :)

Saying a 32W T8 (probably closer to 28W on a typical electronic ballast) overdrives to 54W is only a very rough approximation.

Actually, saying this is not an approximation. It is a very precise measurement from several power meters, and looking at my sample of 12 ballasts. All while being driven from a regulated supply being monitored through the test by a DMM. There are variables to be sure, such as the bulbs used.

Maybe the silver reflector is focusing the light less so it is spread over a wider area.

*All* of the light emitted from the silver reflector was compared to all of the light from the white reflector. It involved some wear on the shutter but I thought it was worth it.

Plus your meter is only accurate to plus or minus 10% at best :)

I have refined my test methods to achieve much, much better accuracy than 10%, and I may have new numbers soon but the fact of the matter is one reflector is so much better that the precise numbers aren't terribly valuable.

Jason

I do wonder what "silver paint" they could be using that would be so much worse than what appears to be a not very impressive white. If the white has a reflectance less than 80%, comparing to the mylar, when cheap white powder coatings are widely used in light fittings to provide reflectances in the region of 90%+.

I've been off this forum for a couple of years, but there was poster "zink", who initiated a thread on overdriving It ran for well over a hundred and fifty posts (people did not want it to drop, so they started another one).

It was truly a classic. So much information about lighting, types of bulbs and ballasts, etc. Some of the discussion was obviously experiences gleaned from pot growing.

I wonder if that thread ran to recent memory or if it eventually died.

Ted

I see the second thread topped off at 98 posts in 2004. Search for "zink" and you'll see it. I have the first thread in my computer somewhere, and if anyone's interested, I would try to pull it out.

Oh, BTW, I have run 7/24 with success. It does speed up the growth, but as the other poster points out, is it worth it? Coincidently, I commented in more detail on the subject in the Tomato forum just earlier.

Ted

Plants will burn if exposed to light 24 hours a day. I keep my grow-lights in the basement and didn't notice once that my timer wasn't working--wasn't turning the lights off at all. And I couldn't figure out why my seedlings, which usually like being very close to the lights, were all getting burnt. I don't think it killed any of them, but it did stress them out quite a bit! And I grow a lot of tropicals which generally like lots of illumination.

I started running my fluorescents 24 hours a day a few days ago after reading the discussion on the tomato forum. I've already noticed a drying and darkening of the youngest leaves, including some dessicated new growth. I'm cutting back to 16 hours a day for a week. I might try going to 18-20 after that, but I don't think the 24-hour regimen is necessary or prudent if you already provide adequate light levels.

Comment on lights and light given off:

Wattage has little bearing on what light your plants are actually getting. Lumens or parr (sp?) determine what your plants will do when exposed to light. An old light will lose intensity as it gets older. (Doubt me? Take one to a pet store and let them test it with a parr meter to see what intensity light it gives off, then compare against a new bulb)

Friend tested a whole series of bulbs for a local club, just to show the contrast. Old bulb gave off 60 parr, new one gave off 274 parr. One year old. Did the same with other fixtures/ bulb styles. And making sure your reflector and any light guards are clean is VERY important too, in terms of intensity. You'd be surprised how much intensity is lost to a dirty reflector or light cover.

Kindergarden analogy: Wattage is like the gunpowder in a shell. Parr is the shot. (sure, more gunpowder will drive the shot further, but if there's no shot, you can dump all the gunpowder you want and it won't affect the target at all) Not a perfect analogy, but hopefully it gets the point across. ^_^

I liked my professor's baby turtles analogy better! :)

A few of us do who grow plumerias. They don't mind it, I would be bold and say they prefer it. Actually, all winter mine are under 24/7 fluoro lighting, one is overdriven(thanks Zink dude.) With plumerias it seems they are healthier when they don't go dormant. All-the-time lighting keeps this from dormancy -much like they are in the wetter tropics(Singapore, parts of Puerto Rico) We noticed this on posts from throughout the world. In the tropics they keep their leaves on under the HID street lights. This is true with mine under fluoros, although they adjust their thylakoids(the dish shaped structures inside the cholorplasts) into shade light collecting configuration -meaning the new leaves that come out are "shade leaves" to collect more light. This allows them to bloom under fluoros(the same way they would in bright shade in the tropics.)

When I bring mine out in the summer there is no need for them to kick into grow mode, they are already there. I am in KC but and my growth is about 3 weeks behind Houston, instead of 8 weeks without 24/7 lighting. In my short summers this is a huge thing. Plus I have blooms all winter long in the garage.

We have one member who is experimenting with 24/7 HID. I have done this for a week and they liked it even more. I would recommend it for cuttings for sure if you can afford it. We have a member on our forum who grows tomatoes in PA with 24/7, said it works well.

I think you have to remember to water your plants because they will need it.

It has us all wondering where the original research is that demands a rest period. This has not been our experience growing plumerias. They are living systems and they adjust.

my two cents...