So my questions are:
How do you setup your lights and fan. How much air and how high? Is there a possibility the seedlings are getting too much light?

TIA,
Dave

If the basement heats up to, say, 75F, then the seedlings right under the lights will be even hotter. First step is to let them cool down and rest at night. Turn off the lights. Turn them off for 8 or 10 hours if you can, or long enough to let the seedlings cool down to about 60F, maybe even a little cooler.

If that isn't enough, then by all means lift the lights. Make sure you have some sort of reflector system and then raise the lights to 6" or 12". With a good reflector you could put the lights on the ceiling and still get nearly the same light, but even with a few bits of white card you can raise them to a foot or so. The lights you have shouldn't be producing enough light to actually damage the seedlings, but the dehydration caused by all the heat and the fun, with no downtime to recover, will be very stressful.

I've read a few posts that some with overdriven fixtures leave the bulbs inches from the seedling and circulate with a fan blowing between the seedlings and the fixtures, my seedlings didn't like that at all. Maybe I had too much air blowing on them. Issue that has me wondering, that the reason for overdriving the fixtures is to generate stronger light to the plants with the bulb at same height and position? Otherwise, wouldn't raising the bulbs defeat the light gain?

I saw a lot of positive post about the light gain, but not many about actual height setup, spacing between fixtures, circulation and whether the extra heat has been a factor with overdriven fixtures. Was hoping that I wasn't to far off base with the setup or learned what I needed to do before I toasted my seedlings :).

Thanks again,
Dave

Light from a point source drops off with the square of the distance. A fluorescent tube isn't a point source, it is a long line. If it was an infinitely long line then the light would drop off linearly with distance, twice the distance, half the light. More importantly, a fluorescent with any kind of reflector is not a point source. The light intensity from a good reflector drops off very little with distance, because all the light remains focused on a fairly small area. Think of a perfectly focussed light source like a searchlight or a laser. The light intensity at one inch is almost exactly the same as the light intensity at ten feet.

The linked thread contains actual measurements and you can see that the light drops off much more slowly than the inverse square law. Notice how it drops off more rapidly with distance. Going from 3" to 6" (double the distance) produces a 33% drop, whereas going from 6" to 12" (also double the distance) produces a 50% drop. This is because a fluorescent tube (without a decent reflector), or a pair of tubes in this case, looks more like a point source when you are far away from it.

In practice, only you can know how the light intensity varies with height in your setup. Ideally, you would measure it since our eyes are hopeless for checking light intensity. The one thing you can say for sure is that the intensity drops off a lot more slowly than much of the lighting advice would have you believe.

"Taking this one step further, you can enclose to the whole assembly of tubes and plants inside a white/shiny box and again almost all the light will reach the plants."

Here is your quote about the white shiny box :). I think I have another project this week...lol.

Dave

For tall plants, you definitely need to do something better than putting the lights very close to the leaves. Did I say that already? I'll use the light source in the link as an example. If you put this light almost touching the top of a six inch tall plant, then the top of the plant gets 4,000 fc and the bottom gets no more than 1,000fc, probably quite a bit less because of shading. This is not healthy. At 3" from the top of the plant, the top leaves get 1,500 fc and the bottom ones get up to 700 fc. The difference is less dramatic but the whole plant is getting less intense light. And it gets a lot worse with taller plants.

To properly light tall plants, you need to provide a light source that gives almost the same intensity at the bottom of the plant as it does at the top, and there are all sorts of ways to do this. BTW, the ability of being able to light the bottom of a tall plant as well as the top is often fuzzily referred to as penetration or penetrance. Much is written about the subject by people who don't understand it :)

One common method, much beloved of pot growers, is to provide the most powerful light source you can lay your hands on and place it at a considerable ditance from the top of the plants. This means that the distance between the light and the bottom of the plants is not much more than the distance to the top of the plants, and so the light is not much less. This is a good method if you wish to provide very intense light over a fairly wide area. Fix a big HID lamp to the ceiling and away you go.

Another method is to provide extra light specifically to the bottom of the plant, either with horizontal lights around the bottom of the plant, or vertical lights at the sides. This method is best suited to small numbers of plants, or even a single specimen.

The last method is the reflector method. A reflector is really anything that gets most of the light onto the plant leaves instead of out the window. It may be a curved shiny thing like a telescope mirror, or a few white flat things like a director's lamp, or a totally enclosed box. When you focus the light into one direction, more or less efficiently, the intensity drops less rapidly with distance. This means that the bottom of a tall plant is lit nearly as brightly as the top. This method is highly efficient but you need to provide the reflectors. I would strongly suggest that all light systems should be provided with at least minimal reflectors even if it is just a white board above the lamp. Modern high-efficiency fluorescent fittings will come with each tube in an efficient reflector although they are designed for an even spread of light in a general downward direction rather than a focussed "searchlight" effect.

For gardening purposes, it's not all that important. But I'm gonna throw this in there anyway.

"Point Source" refers not to the shape of the light source, it's a convention.

When I was a kid, I was fascinated by the way the lights from the Christmas Tree made different color bands of light on my bedroom wall.

With the door open just a crack, each bulb on the Christmas Tree was it's own "Point Source" of light.

So, each bulb was emitting it's own light. It's own 'point source'. On the wall in my bedroom, there was always a multicolor display of light bands. Blue, Red, Yellow, etc.

Because the Christmas Tree was three feet in diameter, the light rays were coming through the crack in the door each at it's OWN angle and separating on the wall.

Thus, instead of one area of 'white' light, I got two dozen bands of colored light. Pretty.

No matter what the source of the light, the Inverse Square law is inescapable.

So, if you have an overdriven tube putting out, say, 4400 footcandles or whatever, the light starts to fall off as it spreads out.

When you put the tube in a reflector, you're just re-jiggering the setup. Now you have the whole reflector as the 'point source' of that light.

But the light intensity will still fall off at the same rate. You just managed to increase the AMOUNT of light you start with.

Nothing can change the Inverse Square Law.

If you start with a HID lamp, and you've got scads of light anyway, the "Gradient" you're dealing with changes the 'penetration'.

For example.

Let's say, on my light rack down in the basement, I have the lights carefully set to no more than 2 inches from the canopy of leaves.

And let's say, for the sake of argument, that I'm getting 4,000 footcandles on the canopy. That's probably high, but I don't have a light meter, it's a guess.

Now, I move the lights up another two inches for a total of four inches.

I just doubled the distance the light has to spread out in.

Now, that's (1/(2^2)) : or 1/4 the amount of light hitting the plants. So now they're getting 1,000 footcandles.

Oops !

Now let's consider a small HID setup. I don't have one, so fill in your own numbers please whenever I type "X".

At a set distance "X" from the canopy, the HID light is emitting, again, 4,000 footcandles.

Let's guess and say that distance "X" is four feet.

Now, if I move that light source another two inches higher, what's the drop in lumens at the 4 ft, 2 inches height?

Not much of a drop. We raised the lights the same two inches, but since the AMOUNT of light was so huge with the HID, the gradient is much longer.

After all, we only increased the height 4%.

To get the same deficit of light with the HID, you'd have to raise it up to eight feet.

In that case, you'd get only 1,000 footcandles from the HID lights also.

Which is why, starting with 50,000 lumens with a HID light lets you illumine the canopy of your plants as well as the lower leaves.

The fall-off in light is small for the extra inches between the canopy and the lower branches.

Actually, I just had an idea the other day for next Winter. Grow a few of the Determinate tomato plants in 7 gallon buckets and slip those fluorescent ring lights around them like stacking doughnuts.

I wonder if those can be overdriven?

Light falls off more slowly from a distrbuted light source such as an array of fluorescent tubes. Once you are far enough away that the light source appears small, then it obeys the inverse square law again. Note that this doesn't mean you get a higher light intensity from a distrbuted source. Quite the opposite in fact. The light intensity far from a distributed light source is the same as at the same distance from an equally bright point source, but the light intensity close to a point source is much higher because the "gradient" is steeper. The light intensity at "zero" distance from a true point source would be infinite, although obviously all available light sources have some size and so you can never get to zero distance. The light intensity gradient from a non-point source flattens out as you get close to it instead of continuing to obey the inverse square law.

Similarly, light from a focussed, directional, or collimated light source does not obey the inverse square law. The inverse square law is a simple mathematical consequence of a fixed amount of light being spread over a wider area as you move further away from the source. For a light source that shines out equally in all directions, or one that shines out equally over a small range of angles like an LED, the illuminated area increases with the square of the distance from the source, so the intensity decreases with the square of the distance. Using a focussed light source such as a parabolic reflector (good flashlight of searchlight) or a laser (directional light), the illuminated area does not increase with distance (not much anyway) and so the light intensity does not fall much with distance. Most reflectors to not produce a perfectly fixussed beam of light (we are trying to grow plants, not burn them!) and so the light does drop off with distance, but nowhere near as quickly as the inverse square law.

Your description of the improved canopy penetration by using a powerful light source at a distance from top of the canopy is correct. However this is a property of any powerful light source including fluorescent tubes. See myth #2 of the ten light myths.

"Any point source which spreads its influence equally in all directions without a limit to its range will obey the inverse square law. This comes from strictly geometrical considerations. The intensity of the influence at any given radius r is the source strength divided by the area of the sphere. Being strictly geometric in its origin, the inverse square law applies to diverse phenomena. Point sources of gravitational force, electric field, light, sound or radiation obey the inverse square law."

Zink

And I was down in the basement checking my tomato plants when it hit me.

Ow !

"The light intensity from a good reflector drops off very little with distance, because all the light remains focused on a fairly small area." -- Shrubs-n-Bulbs

The key words being "good reflector".

My cheap shoplights have only token reflectors.

I have some old magnetic ballast fixtures that have really GOOD reflectors, but I don't raise plants under them. I can't fit more than one per shelf.

So, when I was 'doing the math' I was thinking of my electronic shoplights.

Now, if you folks have fluorescent fixtures with really GOOD parabolic reflectors, the light from those tubes would be focused.

And using the laser reference above, when a light source is collimated or focused tightly, it spreads out more slowly.

A laser pointer that runs off AAA batteries will produce a beam that stays fairly tight for miles.

Pity we can't use lasers to grow our plants !

Now, if I could build a perfect parabolic reflector, two-lobed to compensate for the two tubes each needing it's own focus, then I could probably beam that light at the plants from a foot away with little loss.

But the minimum size for an efficient reflector would be about 12 inches wide.

X=1/4(Y^2) is the equation I always used to use. It gives you a parabola that's not too tight, broader than it is deep.

Which would make it difficult to put six tubes above the plants as I have now. So I'd have less light after all.

I suppose I could design a six-lobed parabolic reflector. But it's much harder to focus light from a tube than it is for a HID lamp.

Each 'pixel' or light-emitting-phosphor analog on the surface of a fluorescent tube is a point source.

Each point source diffuses according to the Inverse Square law.

But imagine this situation. Each point is radiating light. But the points right next to it are radiating light as well.

To simplify matters, imagine that the light from each point spreads out in a cone.

But the nearby points are ALSO spreading out in a cone. So the cones of light cross each other.

Instead of the light diminishing, this overlap slows the process considerably.

And IF you have a good reflector, you can catch the light that does escape and re-direct it on the right vector.

Now say a target is receiving light,1 foot below the middle source point.
Using trig, this target is also receiving light at 5.1 feet from BOTH of the other 2 source points.

Now move this target one more foot, or twice as far away. Now it is at 2 feet.
This movement is at an angle to the other 2 source points. This means the target has now moved to a position 5.4 feet from the outer points.

While the middle point is now 100% further from the target, the outer points are less than 5%further away - only 5.4 feet

Following through with this shows that the drop-off using just 3 source points of light is quite different than the drop-off from a single point.

As you get even further away, you mathematically approach a comparably (but slightly shorter) light travel distances, added to by the source points adjacent to the closest point.

Now imagine a grid of triangles with a source point of light at each intersection. As you got further away, you would have 6 adjacent light sources, to nearly equalize and significantly reduced the rate of fall off.

A ceiling covered with flourescent lights will do the same thing. I peronally did that 15 years ago, in a coal bin in the basement of a house I lived in. I had very little drop-off of light in that room.

Directional reflectors would great, lasers would be dead on.

Zink

I think Zink might just have derived differential calculaus from first principles, but my head hurts so I'm going to assume he's a genius too :)

Most fluorescent lights aren't even trying to achieve a perfect beam, but quality fittings do indeed have two curved reflectors. I imagine they aren't actually parabolic and they certainly aren't deep enough to get completely directional light, but then all they are trying to do is get all the light going vaguely "down" instead of "up" or "sideways". Take a look into your office light fittings (use sunglasses!) and if they're new enough you'll probably see the two curved reflectors.

It would seem that overdriving fixtures is a godsend to aquarium people or for shop lights where heat wouldn't be a concern and need max lighting from cheaper fixtures, but not for me with seedlings.

The worst part was my girlfriend, who was laughing as she watched my changing them back and just couldn't keep her comments to herself...lol. No tomatoes for her!!! :). She thinks I'm nuts...lol.

Thanks for the info and help.
Dave

I would have boosted the ventilation with one mid-sized box fan as the exhaust and used an interval timer to shut down half the lights periodically.

I have one with 14 on/off settings and I see the new ones have 20 on/off settings.

I would think that with half the lights on full time and the other half on half time you'd have happy plants.

You know, I've talked to plants for years. What worries me is, now I can hear them answering.

My original intent on this thread was to get actual examples of other's overdriven light setups(bulb distance, etc.), but that info seems scarce. Better yet after reading all the info posted here, maybe I actually learned something...lol. I figure I reduced my 4000 lumens/sqft to around 2600 or so, hoping that turning the shelf into a reflector box makes 2600 lumens/sqft a good number at 13" away.
Dave

The real test will be with some flower seedling starting to sprout. If they stay compact and don't stretch for the light, I'll call it a success.

Thanks again,
Dave

I bought some hand-cranked winches on sale at Harbor Freight, got some pulleys, and set up my lights so I can crank them up and down.

I try to get the plants just barely under the lights.

(It's a cold, cold, basement, folks).

It takes about thirty cranks to raise the lights five inches or so. Easy to fine-tune.

Some few plants brush the tubes and get spots on the leaves, but they're healthy otherwise.

I had a light rack from 15 years ago, before overdriving was possible. I cleaned the junk off it.

It has three shelves, 17 x 48 inches. It's about five feet high. 2x4 construction.

On the second and third shelves, there's a pair of overdriven fixtures. I bought them for $4.04 each at Home Depot.

That covers about the amount of area needed for a pair of 11 x 21 inch seed flats.

As I mentioned, the fixtures are on pulleys, and connected to a winch.

"Are all your fixtures overdriven? "

On the top, I added a third fixture to widen the area I could cover. I didn't overdrive it, and golleee ! You can tell the difference! The normal lights look cold and dead compared to overdriven lights.

"Do you use a fan blowing on the seedlings? If so, how much air do you blow on them and how often."

I have an old fan I salvaged years ago. Found it in a trash can. An antique, really. Stripped and rebuilt it.

I bought two plastic fans for about $9.99 each. I think the best one says "Lifestyle" on the base. It oscillates and does a good job.

Their advantage is they use only about 17 watts or so.

I was afraid of overheating the antique fan, so I set the three of them up with a lamp timer that turns them on for fifteen minutes, off for half an hour.

You could do just as well with a single larger box fan. I have a Holmes torpedo-shaped fan in my bedroom, $9 at WalMart. Makes lots more air than the smaller ones but doesn't oscillate.

I believe the point in having a fan isn't to have it on constantly, but to strengthen the plants against the wind resistance. And to keep the moisture levels under control, important in a basement.

Also, new T5 or T8 tubes with electronic ballasts achieve light outputs comparable to metal halide. 40,000 lumens from a metal halide requires 420W-480W depending on the ballast, and you can get 40,000 lumens from fluorescents using 416W. So the light is the same, the heat is the same, the spectrum is the same if you want it, and the power is the same. So the only real question is whether you want one metal halide lamp or 5-10 double-tube fluorescent fittings.

I have found out the only way that they are a fire hazard is if you use the improper ballast. Yet also it wouldn't be due to overheating because elecrtonic ballasts by law have to have an inherent thermal protection. "Class P" Which turns off the power when the ballast exceeds 90 degress Celcius and reconnects when it cools off.

I personally would not use the SL.15's for overdriving because it is a series circuit. I use parallel curcuits i.e. the ones when one tube goes out the other remains lit. because they run independently. Two independent circuits together creates more light output with less stress on the ballast. The SL.15's series runs one ballast circuit for two tubes even though you sometimes see one tube running after the other is removed. If you pair all the wires together it will cause the ballast to run harder. Okay...my mind just shorted out...but that is the reason for the fires, because of the type of circuit. Use parallel because two independent circuits help each other to produce a bright light.

-j-

Yes, I know any ballast can fail without notice, but if you have the right ballast and the right wiring, you will have no problem...I have used a Sylvania 4 tube ballast OD'd to 2 Tubes for three years running 16 hours a day for half a year, haven't blown a tube, the ballast runs cool to the touch and haven't had a problem. The tubes go out like any other t8 ballast they arc until the filament cathodes pop.

-j-

VCR's cause house fires ! Yep, just owning one of those things is a fire risk.

Every year I read about somebody's house burning down because of one o' them dang VCRs.

I tell you, it's a conspiracy !

On safety, there's always a risk when there's electricity about. Risk increases if you start rewiring stuff and overloading electrical components. But then sticking an electric light bulb somewhere you are regularly splashing water about always seemed pretty dumb to me :)