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Fluorescent Lighting in Greenhouse

Los Gatos, CA(Zone 10a)

I grow quite a few heirloom tomato seedlings in my small greenhouse. I was taught to use a warm and cool bulb in my fixture for them all season long. This year I switched to two cool (5000-plus) kelvins because I read that it promotes root growth. They did fine until about 3 to 4 weeks into the growing process. They wouldn't turn darker green even though I fertilized them. They did not grow tall and strong like last year's seedlings when I one cool and one warm bulb. So, five weeks into the growing process, I switched out one of the bulbs and put in an Ecolux Plant & Aquarium bulb with 750 lumens but no kelvins listed on the package. It says it contains a combination of phosphors which produce light rich in reds and blues. The plants are starting to grow and green up now. Does anyone out there have suggestions for greenhouse lighting for tomatoes and/or can comment on the above? I really feel like an amateur now.

Gentry, AR

marvelle alls i can tell you is that all i have ever used are the cheap regular florescent shop lights, they work great and will get your seedlings off to a great start. in the first three weeks i also put a regular 100 watt light bulb for the heat to keep the temp from 75 to 80. i start all my seedling that way.

Sarasota, FL(Zone 9b)

Has anybody tried using CFL's (you know - the spiral bulbs we're replacing all our incandescent bulbs with) as plant lighting? They sure seem like they'd be cheaper to buy and last longer than expensive grow lights or regular fluorescents.

Dublin, CA(Zone 9a)

I don't know that they'd last that much longer than regular fluorescents, and assuming you've got a decent number of plants you'd need a lot more of them than you would of the fluorescent tubes...plants do best if they're no more than a few inches away from the lights so a shop light with 2 fluorescent tubes can cover a lot of plants but with the CFL's you'd need a whole line of them to cover that same number of plants.

Durhamville, NY(Zone 5b)

I've used a CFL for a potted plant and it worked. The problem with a CFL is that its ballast isn't that well made and tends to be the thing that fails. I believe a regular fluorescent, especially one with a good ballast, should out last a CFL.

Sarasota, FL(Zone 9b)

Good to know, Doug. Thanks! Longevity isn't really a concern as I don't use them for more than a couple of weeks at a time - just until the seedlings are big enough to transplant to my Earth Boxes.

I tried a CFL and a regular 'Gro-Light' to see which worked better. So far the CFL is superior mostly because it is cooler than the Gro-Light and of course it's using a lot less power as a result. I'm using a 'bright white' CFL, not warm white.

I just generally start a few seedlings at a time indoors, for my outdoor winter veggie garden so one cheap reading lamp does the trick for me. If it's too warm outside the seedlings get r-eeee-aly leggy before they're big enough to transplant. I found out the hard way last fall that if you plant 9 broccoli transplants all at the same time, you get 9 heads of broccoli that are ready in the same week! There are just two of us, so we gave away a lot of broccoli that week! So each month I'm starting just 2 or 3 plants in hopes to stagger the harvest better.

Durhamville, NY(Zone 5b)

I think, for just a few plants, a CFL word work well. I used a CFL in one of those bowl-shaped aluminum utility lightts that have a clip on the back of them to hand from something. As far as I can tell, light output has more to do with how well a light works than it's color temperature.

To the original poster. Color temperature is meaningless for any light that doesn't try to simulate white light. Lumens are a unit that takes into account how human eyes have different sensitivity to different colored light. For example a 10 watt deep violet light is going to appear much darker that a 10 watt Greenish yellow light.

Morrison, TN

I was using 8' tubes in my greenhouse, I had to replace them all the time. I finally went to Daylight 26 watt CFL's, that is what I will use till I find something better.


Durhamville, NY(Zone 5b)

Frequent tube replacements are most likely related to bad or poor ballasts.

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