No expert here..but IDK if lighting is the only issues... low temps will slow the growth of that kind of crop eventually too...

Hope an expert wanders by... Good Luck

Not an expert either but cool white is out, wrong spectrum. There are aquarium type bulbs that have the correct spectrum but not exactly cheap. They also tend to loose intensity and proper color spectrum over time. There is a lot of info out there about flourecent - t5's, VHO, also compact flourescent etc...

If you have the money metal halide is the best bet in terms of cost per watt/output and happy plants. They can be about 10 + inches above the plants and tend to diffuse the light a little better. They certainly help with ambient heat as ontheteam mentioned.

1. The lights inside not only will give you light, also will provide some heat at the same time at 1 watt = 3.4 BTU.

2. I would try to using light fixtures that are as small as possible so that they will not block the little bit of sun you alredy have.

3. If you are going to be doing this every year, try to spend some money and use metal halide or high pressure sodium fixtures. You will save money in the long run.

dcarch

Thanks all. I don't think temperature is a problem because I'm growing cold-season vegetables and the greenhouse is open to the rest of the house; it might dip down into the 40s some nights but nowhere near freezing. Elsewhere I'd read that fluorescents and cool-temp bulbs were good for vegetative growth but not for fruiting and flowering, and I'm just looking for leaf growth; but have you all found that a different spectrum is necessary even for leaves?

Is it possible to run high-output fluorescent tubes in a shop light fixture designed for standard fluorescents?

They require different ballasts.
You can-overdrive normal tubes to get more light.

dcarch

I think you really need to determine if light is actually the limiting factor. My guess on those crops is that it isn't if they are in a greenhouse environment, even a cool one. Yes, they are called 'cool weather' crops, but that doesn't mean that temperature doesn't play into growth rate. They are cool weather crops because they can 1) tolerate cool weather and 2) heat can make them bolt, or go into their reproductive stage. I'd expect shorter, stubbier plants and slower growth rates the cooler it got....given the same light input.

I have a light system in one of my g'houses, but I don't use it for supplementation. I use it for photoperiod control. I have banks of metal halides, mounted high. The light looks intense, but I'm getting little more than twenty foot candles at bench level at night where they were not in direct beam, but I overlapped the beams so that's a pretty good estimate of how much light even those put out. I used light meters at each bench when I installed them to see exactly how much light I was getting. They're also using thousands of watts of power, and you can see the dials spin when I'm using them. I could get lots more at bench level if I went to higher wattage or more lights, but I only need fifteen foot candles and it's expensive enough to get that.

It takes a massive light output to have any effect if you are using them for supplementation because you are going to need more than a 20 foot candle boost. Don't expect to hang over head floursecents , or incandescents for that matter and have much effect. For them to have an effect they'd have to be placed close to the plant's surface. I mean CLOSE. If that is the case, then they'd work but you'd have to consider the safety of using lights next to a crop with water being in the environment. Most people use them on little grow benches, or for inside growing with a few pots or plants. If you are only growing a very small crop it may be an answer, but if you are growing whole benches of them, don't expect a cheap installation or power consumption. It isn't. That's why I do not grow fruiting vegetables in winter. I have some cool weather veggies up on my benches now to take adavantage of the fact I'm already heating one g'house for seed starting my spring line. For those, I don't use supplemental lighting and they grow fine at around fifty five nights and overcast days, and ambient solar gain on sunny days.

I'd suggest you might want to run this by your extension agent (it's free) to see if he/she can find for you what light requirement your plants need. Those figures are available. Then IF you need lighting, you can go from there.

calliope,

I don't mean to sound demeaning, but suggesting you are using thousands of watts of power and only getting 20 foot candles of light is just plain wrong. And saying you only need 15 FC is also wrong, unless you are growing plants that do not like light.

Maybe you mean 2,000 FC?

Mike

Read up on Eliot Coleman, he says that light shouldn't be a factor, it is more the temperature. I would do an experiment. I would work on raising the temperature first and keep it at a higher low temperature. Anyway, the shortest day of the year is coming up, December 22nd. After that, the days start to get longer. Somewhere in early February, we start getting the first real "Growth Days" in terms of length of days. I am no expert and I can only share what I have read. I know that my spinach in my unheated high tunnel isn't growing much, but it is currently 7 degrees outside, last week it was -7 or -9! It tastes wonderful! However with the sunny days, it will warm up to around 55-65 degrees.

I get about 50,000 lumins from my 400 watt MH bulb.

dcarch

Does anyone happen to know if putting that silver mylar on the north side of a greenhouse will increase usable light to any degree? I'm talking about those cheap $3 emergency blankets, thin, crackly, shiny, and just using them to reflect incoming light, sort of to get 'double duty' out of it.

Any thoughts?

Sue

Mike, in my post I said I did not use my lights to 'grow' plants, I said I use them to provide 'short night' response in my photoperiodic plants to postpone their bloom times. For that, I don't need 2K foot candles, I need 20 foot candles.

For the purposes of determining the quantity of light your plant is actually getting you can't just spit out the wattage or lumen rating output of a bulb as rated on its package. For instance, a hundred watt, unshielded incandescent bulb, ten foot away from an object will only provide about 1.5 foot candles as measured at that objects surface. That isn't much, is it? So, you can't just say a lamp has X lumens and have that mean much of anything. That's the potential output of the bulb. What you are interested in are the readings at leaf level, measured in lux or light density and that is going to vary greatly depending on how far away the light source is, what design the reflectors are, angles, intensity at various points of the cone of the beam. Yadayadayada. And if you think you are actually doing much trying to supplement the natural light by hanging a few shop lamps from an overhead beam in a greenhouse with a flourescent tube in them............well, it's not going to hurt anything, but it probably has negligible actual benefit to the plant.

So, if you are really needing to provide lighting by which a plant will actually grow.........then your supplemental growing light has to be quite close to the plant, or the output has to be considerably higher than you think if mounted from overhead beams. The only way to really tell is to meter it out at various points in a greenhouse. That's why I suggested the poster find out what intensity of illumination leafy veggies really take. If she/he can make do with natural light, it would save a lot of money, and I suspect they'll grow just fine without supplementation.

That's why in all but special circumstances where high light levels are absolutely necessary for producing certain plants in a winter setting, most growers do not go the expense of installing supplemental lighting. It's expensive to install and it's expensive to run, unless you are just interested in starting a few seedlings or a very limited collection of conservatory plants.

"Posted by belgianpup Wa/Zone 8 (My Page) on Wed, Dec 16, 09 at 1:10

Does anyone happen to know if putting that silver mylar on the north side of a greenhouse will increase usable light to any degree? I'm talking about those cheap $3 emergency blankets, thin, crackly, shiny, and just using them to reflect incoming light, sort of to get 'double duty' out of it. Any thoughts? Sue"

Yes, it would help. Try not to use the kind that is gold colored, use the ones that are silver colored.

However, consider using Mylar mirror sheet/film. It has a much higher reflectance and it lasts much longer. I use Velcro to hang them.

I think even better would be to use aluminum foil faced foam board.
I got 4' x 8' x 1/2" boards from HD for about $12 each. These are the ones with a very reflective shiny foil facing. It will make a dramatic difference to the usefulness of your GH, especially if your GH is not insulated.

dcarch

Calliope,

Veggies that need the most light, such as tomatoes and peppers to produce fruit, require a total of about 15 moles a day at the least, 20-22 to be real productive. A mole is an accumulation of PAR light intensity in an hour. 2,000 foot candles (or ~21,500 lux) at the plant canopy of sunlight will supply about 1.42 moles per hour. 2,000 FC of HPS light will give you .96 moles per hour and MH equals a bit more - 1.02.

On a sunny day in the middle of December in Cincinnati, I get somewhere in the neighborhood of 14-15 moles in a day. In a couple of weeks, maybe three, I should be able to pick up at least two moles a day, as the sun will be higher in the horizon so houses don't block the light from reaching the GH.

Mike

I do not do vegetables in a winter greenhouse, Mike. Other than some cool crops(leaf lettuce and also celery) for my own use because I'm heating it for a winter crop anyway and natural daylight is sufficient for all of the plants I winter grow. I only use lighting for night interruption and I use a five thousand watt system and it provides a minimum of 15 foot candles at canopy because they are mounted on overhead beams and lateral throwing beams quite a distance. I don't do crops requiring supplemental lighting because in my latitude, it's just not cost effective and my business is profit-driven. I overwintered some tomatoes and peppers one year I had as patio pots, and it just wasn't worth the effort because although they didn't die, the fruits were the size of ping-pong balls.

I'm glad you seem to be having success in doing winter tomatoes.

Are you sure you are getting only 15 foot candles with 5,000 watt lights?

I am getting 50 foot candles with a 25 watt CFL from my desk lamp.

dcarch

Calliope,

Thanks for the thoughts but I do not want to mislead anyone. I am having great success growing tomato plants. I'm having little success growing tomatoes. There is an iron-clad rule that it takes X amount of sunlight or artificial light per day to grow plants to complete production. (Do a Google search for Daily Light Integral Moles.) In Ohio, in December, we plain don't get enough. It would take quite a bit of supplemental light to achieve the 18-22 moles per day needed. This doesn't mean it is economically unwise - I can heat my GH for an average of $3/day and if I was to install enough lights to give me the 18-20 moles/day I need would cost another $7/day. That's about $20/wk. so I can raise 40 tomato plants or about $450 over a 5+ month period. Of course, during that time, I will not need some heat for few-many hours or lighting for few-several hours per day. But 40 good tomato plants should provide, at the least, 800 pounds of tomatoes. At $1.25 per pound - a real steal in winter in Ohio, that's a grand. Grow a decent plant (25 pounds) and charge $1.50 per pound, still a steal in December-March and that's $1,500 or more than three times the cost of utilities.

My plan is to have GH toms ready to harvest from Oct-Dec. Shut it down for the most part from mid-Dec to mid-Jan but grow about 30 plants upstairs so they provide fruit from mid-Dec to mid-March. Then switch back to GH production for mid-March through July, with the outdoor garden taking over for the rest of the time.

There really isn't that much difference between success and failure when it comes to growing plants. Just where you plot the point on the same line!

Merry Christmas!

Mike