This is something I posted back in January. It may or may not be helpful.

There has been a lot of research that identifies which plants need what sort of light (wavelengths) and intensity to germinate, grow, and flower. Generally speaking, plants utilize two sorts of light and for discussion I will call them "red" and "blue." The wavelengths between the red and blue peaks of the spectrum are more what our eyes see. This "visible" wavelength is something like 430-660 nanometers. At the extremes are UV and infrared, and neither of these is beneficial to plants. An overabundance can cause plant mutation and even death. UV is less than 400 nm and infrared greater than 700 nm. Excess UV mutates cells. Excess infrared burns plants. (For orchid growers and many other tropical plant growers, this infrared is what "sunburns" our plant's leaves.)

The so-called "visible" light, the range that our eyes can actually see, is not really beneficial to plant growth/bloom. That means that the vast majority of incandescent lighting won't help you much.

Most plants need a good measure of both red and blue spectrums. The useful blue is 400-450 nm and the useful red is 650-700 nm. These numbers become important IF you want to use some sort of Gro-Light.

For spring and summer bloomers, during the fall our light will move gradually from the red spectum to the blue spectrum. I'm talking about the Northern Hemisphere. As the sun gets lower in our southern sky, the blue spectrum increases. The blue triggers the plants to "change gears" from growing (vegetative) to blooming (budding). For fall/winter bloomers, just the opposite occurs. During the spring/summer, as the sun moves more overhead, there is more of the red spectrum and this triggers the plants to bloom in the fall/winter.

Paul, thank you for this info, though I am some what confused. I have never heard of par. You have a great setup. You sure know what you are doing. Are you a commercial grower? What do you grow?
Ken, I understand what you are talking about. The seedlings are already growing, I just want to keep them growing during the winter. I'm not looking for blooms at this time. I'm growing Kedrostis, Ipomoea, Ibervillea, Euphoria, and a few other caudex forming plants. There are under 10 plants of most species.
As for going to specialty store, it is hard for me. I depend on my sister and dad for transportation. I don't ask to be taken to a lot places out of courteousness to them. I am grateful for where they do take me.

Reine, I think you, like the vast majority of us, will do just fine with some regular "shop lights" -- I would suggest, if possible, keeping the winter temp fairly cool for your plants, to keep them somewhat dormant, so they don't put on a lot of weak growth.

Rick, that was a very good comment about the big box stores, which I totally agree with in principle and I wish I could say that I never shop at them... Unfortunately, the reality for many of us is to buy where we can find something cheap, or not buy at all. This is a huge conflict for me, because I know that these stores result in many smaller local businesses being driven out, and then we are at the mercy of whatever they decide to charge. I'm not sure what the answer is to this dilemma!

Finally, Ken -- that was also good information about the lights, someone should really put all this stuff together into an article! (hint, hint...)

Yes, I grow commercially, so I apologize if I've taken this question far beyond what was relevant. I debated responding at all, but thought I'd put in my own setup as another example. I think Ken did a great job explaining light usage, though I might quibble with the blue/red generalities.

PAR is Photosynthetically Active Radiation and refers to the light which actually can be used by the plant. This is different than Visible Light, which is viewed by your eyes and usually the only thing indicated by the lumen ratings on light bulbs. It is also different than total output from a light source, which often includes ultraviolet and infrared. Much of the lighting industry rates efficiency in terms of the amount of visible light (lumens) produced from a source per (electrical) energy used. What we care about for growing plants is the amount of PAR produced per energy used.

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This is complicated and more information than needed in a small setup, so feel free to stop reading now, but I'll try to explain what I was talking about earlier for the curious:
The PAR curve doesn't directly match the chlorophyll absorption spectra because of secondary light gathering pigments such as carotenoids, and the fact that lower wavelengths carry more energy but don't necessarily contribute more energy to the plant. However, the important thing in the light source is to make sure that the emission spectra (usually available from the manufacturer) fall within the large parts of a standard PAR curve (easily found with a google image search). Fluorescent bulbs in particular tend to only radiate in very narrow bands around their constituent phosphor emissions, and if these bands aren't on your PAR curve, or are in parts of the curve that are only weakly utilized, they're just wasted energy.

Individual plants, based on their photosynthesis profiles and the pigments they produce, have different PAR curves, and these can vary with maturity, season, and life cycle. Most of the time, though, you can get away with matching to a generic curve, and most daylight rated bulbs have emissions spectra within the PAR curve. Most of the time it doesn't matter. But these gross estimations are part of the reason why it often doesn't pay to mix warm and cold bulbs or worry overmuch about the light fixture, unless you really plan to do the research and adjustment to properly take advantage of them. You'll need spectra sensitive light meters to do more than stab in the dark (metaphorically) toward the results you're looking for. Even then, savings can be slim and results difficult to measure. If, on the other hand, you're starting tens of thousands of plants, then power savings, growth consistency, internode management, and lifecycle triggering all make it worthwhile to really pay attention to your light.

Yes, those things are important for professional growers who need to produce perfect plants. Their livelihood depends on it. But for home growers like me who just want to keep something alive over winter, a little fluorescent light supplement will do just fine.

Here's a good one page overview:
http://www.littlegreenhouse.co...


Karen

Great explanation Paul, thank you.

eclayne said:Great explanation Paul, thank you.

Paul, even though most of us will never take it to the level you have, it never hurts to have more information !

Great information, Paul. My post was geared towards the average hobbyist (like myself). Entire books have been written on "light" and many lengthy articles have been written on how light affects plants.

drdawg said:Great information, Paul. My post was geared towards the average hobbyist (like myself). Entire books have been written on "light" and many lengthy articles have been written on how light affects plants.

It's really an interesting subject. I've read a few books about photoperiod, which were mostly about the effects of light on humans, but the effects on plants are always mentioned too . I'm actually using a bright light box to try to change my own internal clock. My sleep schedule has been out of sync with the rest of the world for decades. I'm really more on DST all year, and when the rest of the world turns their clocks back in fall, my internal clock just won't change.

Plants have their own circadian cycles, too.
http://en.wikipedia.org/wiki/C...

Karen

kqcrna said:
I'm really more on DST all year, and when the rest of the world turns their clocks back in fall, my internal clock just won't change.

That's funny, Karen. I'm the other way 'round, which is probably why I hate the whole "Daylight Saving" concept.

I just wish that there were some option other than fluorescent tubes. I hate the darn things; I'm a klutz and can never get them into the fixtures properly.

Yes, the tubes can be a little clumsy to work with. But overall, I REALLY like my t5s a lot.

Karen

Thanks Paul. I did understand your info a lot better this time.
Sandy, you said "I would suggest, if possible, keeping the winter temp fairly cool for your plants, to keep them somewhat dormant, so they don't put on a lot of weak growth".
This is the way I keep the plants for the winter, if I treat the seedlings the same way will they need extra lighting? Since I am not starting seeds do I need any extra light?

Reine

What kinds of plants are you trying to grow, Reine? Do you have really good window light in your home? I don't. We have a giant maple tree on the SW (front) side of our home as well as a porch with a roof, and my nieighbor's tall trees block the direct sun to the back (NE) side of the house. If you have big windows with good sun that can help a lot. But in the dead of winter, when days are so short, a little supplemental light can make a huge difference to most plants. Most aren't going to be that picky about the specific color of light You are fortunate to live in a warm climate where plants can remain outside much of the year where they'll get the best possible natural light. Up here in Ohio, not so much.

Also consider: what kind of conditions do you have in mind? If you want to grow a bunch of stuff on a big table in your basement, one MH or HPS light hung from the ceiling might work out fine. If you want them on shelves, fluorescent tubes fit the bill. The fluorescent tubes just need to be pretty close to the plants (a few inches above). My high output t5s have worked great for anything I've tried to grow. Simple shop lights seem to work fine for most plants.

Karen

Karen, I have seedlings of Ibervillea, Coccinia, Kedrostis, Gonolobus, Pachypodium and a few other caudex forming plants. There are approximately 10 seedlings of each species. So I don't have a whole lot of seedlings.
There is a large window facing south and that room is the warmest.
I have another room on the east side that stays cool, all my dormant plants go in there.
I live in southeast Texas, zone 9a, we have had to use the A/C in the winter before. But there can always be a frost in early winter and it can get down right cold in January and February.
Y'all think the south facing window will be enough, or just let them go dormant? This is my first year on growing from seed.
Thanks for all of your help.
Reine

Geez, I've never grown any of those so I know little about them. My guess is the warm south window would be preferable. Basically, I think any plant will do better with a little supplemental light in the short days of winter though, which can be as simple as a CFL light or shop light for a few hours a day. If you can't swing it, you might try a few in each room and see which does better. In your climate they might get by just fine in a south facing window. And you probably get warm days in winter when they could take field trips outside into the full sun for a few hours in an afternoon.

But they'd probably like a little extra light.

Karen

Thanks very much, Paul!

I have a south-facing window, and tried to keep some seedlings there one year. The seedlings didn't seem to like it very much in late winter when the sun was low in the sky most of the day.

I think they got too hot in the daytime, and chilled at night. It's an old manufactured house with some drafts, and that window might not be well insulated.

Karen and Rick. I probably should buy the lights. I think some of the seedlings may be able to go dormant and be ok. But a few will need to keep on growing through out the winter. Most of these plants are from Africa.
Reine

Here are some of the seedlings









.

I love baby pictures!

Karen

Interesting! Especially the first picture, with the seedling stems that look like tree trunks (the caudex, I guess). Gonolobus ?

If it is this plant, the database needs your seedling pic!

http://garden.org/lists/plant/...

Thanks for y'all's comments on the seedlings.
The Gonolobus cyclophyllus is now known as Matilda cyclophylla. Or maybe both names have been in use for quite a while. I bought the seeds as Gonolobus and have since found out the correct name is Matelea.
Rick, I will get a better photo and add it to the Database.
Reine