Many T8 tubes for "human" lighting are now 34W, 32W, or even less (26W is one of the latest most efficient tubes). The intention of this is that they produce the same amount of light as older 40W tubes, but use less electricity, so that they can be used to directly replace tubes in older fittings without you needing sunglasses in your kitchen :) That isn't ideal for plants where you'd probably prefer more light, but they will still work just as well as fluorescents worked ten or twenty years ago.

Cheap tubes might not be reaching their rated lumens, they might not be working well with your ballasts, or they might be giving off a more yellowish light that just appears dimmer. What are you comparing them to?

I have found that most cheap fluorescent tubes are a false economy. They don't last as long and they are less efficient so you are spending more on your utility bill. A typical 40W tube uses nearly $100 of electricity by the time it burns out, makes sense to spend an extra buck or two to get an efficient one.

Okay, that's what I needed to know. I think I'll spend the extra $$$ and replace these tubes - maybe use them elsewhere in the house but not for my precious seedlings.

shrubs,

The 34w lamps are a U.S. innovation which appeared during the energy "crisis" of the '70s. They were supposed to reduce power consumption and operate on existing 40w ballasts. Unfortunately, they reduced light levels even more than they reduced power consumption, and they often did not work on existing ballasts. The engineers had such a difficult time even getting them to start that they had to add a coating of tin to the lamp to increase the capacitance enough to encourage the initial arc. They also need to be close to the metallic reflector for the same reason. After they appeared on the market, ballasts were designed to accomodate them. Ballasts would state that they operated 34w lamps, if they could do so. Still, they were a poor idea.

The 25w 48" T12 lamps sold here in the U.S were created solely because of a 28w limit. When the F40T12 lamps were being legislated to be more efficient, the government allowed lamps below 28w to still be manufactures and sold. Lighting manufacturers came out with a 25w lamp design to be put in 25w shoplights as a result of the legislation. They, too, are really, really lousy - too dim to be useful.

I have seen you say that the T12's are old, inefficient and dying technology, in different words however. In reality, the F40T12, when using the SAME phosphors and manufacturing techniques as the current triphosphors, are slightly MORE efficient than the F32T8 lamps. I could go into great detail here (and quote the lamp deigners themselves), but basically the T8s are currently preferred for 2 reasons. Mainly, the lamps have much less surface area to coat with the better, expensive phosphors(cost), and second, the luminaires and reflectors have improved illumation possibilities with the narrower tubes(design). There definitely are very good, expensive, T12's on the market with as good efficiency as the T8's. And, more T12's are showing up as they improve their efficiency to meet government standards.

To see exactly what I mean go to http://groups.google.com/group/sci.engr.lighting
and in the "Search this group" enter the search term "10 watts per foot".
You will learn a lot from the results.
Victor Roberts is a PHD Lighting Engineer who designed many GE lighting products.
Jeff Waymouth is a PHD Senior Lighting Engineer for Sylvania, his father was also very well known in the field.
Terry McGowan is the Manager for Worldwide Application Development for GE Lighting and Director of the Engineering & Technology for American Lighting Association.
There are others in this newsgroup who also design the products you buy. These discussion are untainted by any Marketing or Third Party Resellers.
You might even search for "Zink" in this newsgroup.

Zink

Zink, I think you're holding on to your dislike of something that happened before many of us were born. Go out and buy a decent 32W, 34W, or even 26W tube and they actually do what they were always intended to do, that is produce the same light with less electricity. Almsot every 40W office fluorescent in the country is now 32W. I agree that the 34W tubes that zone3er has may be an old design with poor light output or may just not work well on that ballast.

As fot T12s being obsolete technology. T12 may be the theoretical "best" size for certain tubes, but if you you can't find a good one because hardly anyone makes them then they are effectively obsolete. Government regs or not, I can only see T12 continue to decline. Plus their large size will always make them unattractive to a plant grower for the same reason that the energy-saving 32W and 25W tubes are: low light intensity.

Shrubs,

Absolutely! Inefficient bulbs that were supposed to be aa "energy improvement" will always have "least-favored" status with me. I am not sure what 34w bulbs you are talking about over there, but the 34watters(which are T12's) currently being sold in the U.S. are better that they were, but still not as efficient as most of the others available. The original 34watters (which I will always dislike) were awful. Still, why put a 34wT12 in a in a fixture that could also operate a 40wT12 with better LPW.

You are not to blame for not knowing what has gone on in the US for decades. There are millions of 48" T12 shop lights here that have been the mainstay of fluorescent lighting for a long time. The T12's may have been legislated into submission for a while here, but they are making an noticeable comeback. We have new, much more efficient, extensive lines of T12's now available at stores here in the states. One large hardware store chain, Home Depot, sells Philips "Home Light" line of very efficient T12 lamps for the large base of 40wT12 fixtures. Philips happens to also have several types of higher output 40wT12 lamps (Ultralume, Advantage) available here. To top it off, there is a whole new generation of 40wT12 electronic ballasts being produced by nearly every ballast manufacturer. All of these are the eventual result of the mandates in efficiency legislated by our government. The new replacements for the old technology are arriving in full force, and very large number of them say "40wT12" on the box.

These lights certainly aren't "unattrative to plant growers" over here. There are what most plant growers here have bought. And the options are getting better all the time. I'm not saying anything bad whatsoever about T8's, mind you. They are a luminaire designer's preference. I just know what most people in the states have available, and have purchased.

I have T12,T8, and T5 lights and fixtures. All have their place.

Zink

I added up the total wattage of my single-shelf setup: 2 x 15 watts for the two heat mats, plus 2 x 40 watts for the lights: I run the heat mats 24/7, and I run the lights about 12 hours a day (from when I get up until when I go to bed or it gets dark, whichever comes later). It's still less than leaving one 100-watt (incandescent) light on all day, so I'm not going to worry about it. Furthermore, the setup doesn't go on until December, and shuts down no later than April.

Lisa

Zink, quick question...

I am having hard time finding T8 flourscents in my local Home depot. T12 is more prevalent. Does overdriven T1240W performs as well as 40w T8, performance wise?
Also on the new SL15 ballasts, it has 2 yellow wire. The overdriving diagram shows only one yellow wire, is it ok to attach both yellow on one side of 2x overdriven flourescent tube? or, you recommeding cutting off one of the yellow cable? To be more clear, on one side of the tube we have (blue-red and blue-red) on the other end the 2x has (blue-red and Yellow), but instead of one yellow wire, could I connect both yellow wire? Are the 2 yellow wire coming out of the ballast identical?
Energy consumption wise, does 1 overdriven tube consumes two times the electricity of a identical single not-overdriven tube? Or, is it greater or, less?

Sorry too many questions..I did not mean to hijack this thread...sorry.

Here is a link that might be useful: Over drive...

sanj,

I have purchased maybe 2 or 3 dozen of the HD fixtures(w/ SL-15 ballast) at different times over the last couple of years. All of the HD fixtures I have overdriven had the original SINGLE YELLOW wire configuration. The last few I purchased are still in the box, and may be the DOUBLE YELLOW wire versions, but I can't recall. I did look in the box when I purchased them to be sure they were the correct ballasts, but I am at work right now, and cannot remember if they had 2 yellows. I did know, from others posting here, that the HD fixtures now had the 2-yellows, and I intended to try overdriving them to be sure that they were the same wire, as you alluded to. I do believe that several regular contributers to this forum have already overdriven this ballast, and I am quite sure it works by either tying both yellows together, or just taping one off, as they are most likely the same wire. I am 99% sure of that.

As far as using a 40wT12 lamp after overdriving - YES! The 40w lamps are definitely brighter with a 2xOD ballast. I have also tried using a 40wT12 that no longer worked in a regular magnetic ballast, and it lit up like a new bulb in the overdriven fixture!

Zink

I've gotten great results using Gro-Lux Standard and especially Agrosun bulbs. They're pricey but so's electricity (as shrubs points out) and your time.

So suppose you're a plant grower and you want to buy some nice bulbs for your 40-watt, 4' T12 fixture. You can buy a lousy $1 budget cool-white bulb and get spindly plants, or you can pay $15 for an Agrosun and wonder if you overspent. What's the best choice for those who don't need that last 2% and don't want to overdrive or rewire their fixtures?

Here is a link that might be useful: Fluorescent grow lamps