Lights for starting from seed.

[Hotwired]

Electrons & ions (charged atoms) collide with gaseous mercury atoms, which then releases UV photons. Since UV light is not within the visible spectrum, the inside of the tube is coated with phosphor, which glows when struck by UV light. The Phosphor does two things... it provides visible light, and depending on the phosphor, does what is called a Stokes shift. Fluorescent tubes output blue light, and by changing the phosphor coating they can "shift" the color toward the red for warmer lights.

Now as to why the bulbs lose brightness over time, the phosphor degrades over time by being constantly bombarded by UV photons. T-8 bulbs have a different type of coating than T12's, and therefore has less loss. The T5 bulbs are even better relative to loss of brightness. Of course the better the coating, the more costly the manufacturing and coating process.

[artis]

Originally Posted by Hotwired

Can you send me the link for the PAR curves. This is not a curve that I've ever seen. As I said, I'm an optical engineer and not a botanist. Are these photosynthesis saturation curves in Watts per square meter, and at what stage of growth. The saturation curves for foliage growth is much different than for flowering. I was aware that each plant species has it's own PAR and the "Accepted Par Curve" is a composite or averaged curve. I'm trying to expand my understanding of PAR, so I'd like to see your link to the Inada study. I've seen a study by AA Tikhomirov that I'm still trying to digest. I can design optical coatings to manipulate light to do most anything, but plant biology is still a bit like Greek to me, but I'm trying to learn more.

Hotwired,

I am not a botanist either, just trying to learn and understand this complex subject myself. Here is a link to a PAR study on a bean plant:
http://www.ncbi.nlm.nih.gov/pmc/arti...396523/?page=4

The biggest surprise to me has been how efficient photosynthesis is with the green light, even though it is reflected away to a significant extent. This may explain why triphosphor fluorescent tube lights are so great for growing seedlings, even though their main emission band is in the green region. Here is an in-depth article about the role of green light in photosynthesis:
http://pcp.oxfordjournals.org/conten....full.pdf+html

There sadly seems to be a lot of deliberate misinformation about PAR propagated by the sellers of overpriced LED grow lights. They will pretty much tell you that plants only need a narrow band of blue and a narrow band of red, and some special, secret wavelength that they include in their products but nobody else knows about.

As you have mentioned in your posts, different wavelenghts appear to control different stages of plant growth, and plant species differ in their light requirements. This whole subject seems complicated yet intriguing to me.

[dice]

the phosphor degrades over time by being constantly bombarded by UV photons

Ok, thanks.

So you can make a mercury-free, high-efficiency flourescent
light by putting uv-emitting leds inside a phosphor? Where
the "fail" in MTBF would be "become too dim for the application
over time"?

edit:
Actually, I guess industry already has these:
http://upload.wikimedia.org/wikipedi.../62/Br20_1.jpg
(Probably more expensive to manufacture than an ordinary
flourescent with all of that hardware in there.)

[tsipgolf12]

Originally Posted by Hotwired

You want the 6500K Daylight Bulbs, not the 2700K Warm. The warm are for flowering. Pack the CFL's as tight as possible and build a reflector covering it with aluminum foil.

BTW if it's your first time starting seeds inside, there's a lot of good info on Tomatoville. Here's my method.

A JuryRigger's Guide to Seed Starting

This is the 2nd or third time I have studied your seed growing outline. I believe I read it in another thread or am simply reading it again. You are so knowledgeable on the light requirements and the practical approaches for us beginners and so willing to devote your time and knowledge to share with us. I learn something knew each time I read it again. Thank you for giving us a head start by sharing your experience. My future tomato seedlings
thank you as well.

RWG

[Wds83]

I just built a quick light stand. I bought T-12 fixtures because they were cheap. I'm only using this setup until it gets a little warmer and could use my greenhouse. I bought 2 Sunshine bulbs and 2 regular cheap bulbs. Will they be good enough to get things going? Also using a heat mat.
Thanks
Bill

[Cole_Robbie]

Nice PVC work. You can make it a shelf when you're done.

It looks ok to me, as long as you can keep the cells moist until the seeds sprout. I would put your cell trays in web flats; then you can dunk it in a bin of water easily for watering, and it's easy to move around.

The speed at which they sprout will likely be affected by the ambient temperature of the garage, which I assume goes up and down with the outside weather. If your weather is like mine, it's been all over the place lately, 35 and snow today, 60 and sunshine forecast for Saturday. If you happen to have a sunny day and your greenhouse is warm, it would be worth the effort to carry the trays out there just for the day to take advantage of the free heat.

[Wds83]

Thanks Cole.
I do have cell trays, just put the empty tray there for the pic.

I didn't glue any of the PVC so I can add a shelf on top. All I have to do is replace the 90 degree elbows on the ends with T connectors. I also used 1" 1/4 PVC instead of 1" to give it more strength.

I think I might add one more light to get a better coverage. Does it really matter what type of bulb I use?

[Hotwired]

Originally Posted by Cole_Robbie

I would put your cell trays in web flats; then you can dunk it in a bin of water easily for watering, and it's easy to move around.

Soaked trays get pretty awkward to move around. I cut the corner cell out of the multi-cell liners, and bottom water through the opening. I have 71 cells instead of 72, but I don't have the trays buckling from the weight when lifting them, or sloshing around making a mess. Always bottom water or you'll have damping off.

Originally Posted by Wds83

I think I might add one more light to get a better coverage. Does it really matter what type of bulb I use?

6500K bulbs for starting seedlings.

[dice]

You want cool white or daylight bulbs for seedling growth. Warm white
are less effective for that phase of plant growth. If you are looking at
"color temperature" ratings on the packages, look for "6500K".

[Cole_Robbie]

I don't even try without a web flat around the cells:
http://www.growerssupply.com/farm/su...51_109087.html

If you get a bin that it fits into, it's an easy way to dunk it for watering. I 'fertigate' with some stinky Alaskan fish ferts.

Besides benefits to the plant from bottom watering, it's a lot easier on me. I am trying to make all of my greenhouse benches into flood and drain tables so that I can water a lot of plants quickly.

[ChrisK]

Posted link below previously in an older thread so here it is again. Cool white fluorescents work perfectly well for starting seedlings and are usually the cheapest.

http://www.uaf.edu/files/ces/publica.../HGA-00432.pdf

Originally Posted by Wds83

Does it really matter what type of bulb I use?

[GoGayleGo]

Originally Posted by Wds83

I just built a quick light stand. I bought T-12 fixtures because they were cheap. I'm only using this setup until it gets a little warmer and could use my greenhouse. I bought 2 Sunshine bulbs and 2 regular cheap bulbs. Will they be good enough to get things going? Also using a heat mat.
Thanks
Bill

I may have to "borrow" this idea, thanks! I tried to throw together a light stand with PVC, but mine was unstable (hubby made sure to tell me about that!). This looks much sturdier, and I don't need too much more PVC to pull it off!

[Wds83]

Originally Posted by GoGayleGo

I may have to "borrow" this idea, thanks! I tried to throw together a light stand with PVC, but mine was unstable (hubby made sure to tell me about that!). This looks much sturdier, and I don't need too much more PVC to pull it off!

GoGayleGo,

Here is the material list:

2 - 10' (1"1/4 PVC)
6 - T Connectors
4 - 90 degree elbows


__________________________________________________ ___________________

Cut lengths for PVC
7 - 19 inches
4 - 24 inches
4 - 3 1/2 inches

If you want to add another shelf just replace the 90degree elbows with T Connectors. Also if you want a tray to fit on the shelf cut the 3 center braces at 15 inches instead of 19"

[GoGayleGo]

Originally Posted by Wds83

GoGayleGo,

Here is the material list:

2 - 10' (1"1/4 PVC)
6 - T Connectors
4 - 90 degree elbows


__________________________________________________ ___________________

Cut lengths for PVC
7 - 19 inches
4 - 24 inches
4 - 3 1/2 inches

If you want to add another shelf just replace the 90degree elbows with T Connectors. Also if you want a tray to fit on the shelf cut the 3 center braces at 15 inches instead of 19"

Thank you so much, I'm sure I'm not the only one who finds this info helpful!

[Hotwired]

Originally Posted by ChrisK

Cool white fluorescents work perfectly well for starting seedlings and are usually the cheapest.

Chris, I couldn't get your link for U of Alaska to work, but I don't agree with Cool White (4300K) being best, unless you are growing flowers. Then it is ideal. I always used "Natural" bulbs, until I made up a graphic, overlaying Color Temp, Wavelengths, and the Plant's PAR curve. It was a big eye-opener. I'm a retired optical engineer, so I am a bit anal over anything related to light and tend to look for perfect solutions. Unfortunately, with growlights, there are no perfect solutions. Almost anything will work, but some will work a whole lot better than others.

Fluorescent Bulbs are available in 4 basic colors:

Warm White = 2800K-3000K
Cool White = 4100K
Natural = 5000K
Daylight = 6500K

The Daylight Bulb (6500K) is almost perfect for starting plants inside, since the Blue PAR for foliage and plant growth peaks at about 6600K. For Flowering, the Red PAR peaks at 4300K, so the Cool White is ideal for Flowering and the Red-PAR coverage. The warm White bulb spikes in the IR, and has fair coverage of the Red, though not as good as the cool white for flowering. Both the Cool White (4100K) and the Warm White (3000K) have extremely poor coverage in the Blue portion of PAR. The Daylight Bulb at 5000K is the worst because it peaks at the yellow-green point within the PAR curve, an area of the spectrum which the plant uses very little of that color light.