dmr
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green house vs house light

Just started my seeds in my peat pots and am wondering if I need to put them in a green house when they sprout or just leave them on the kitchen table and leave the light on.

DoubleDogFarm
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South facing window would be better, if you don't have a greenhouse.

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rainbowgardener
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You didn't say seeds of what; it makes a difference, because different plants need different amounts of light.

However, putting them on the kitchen table with the light, which I assume is a ceiling fixture, on is worthless. Light diffuses by the inverse square law, meaning if a light is moved twice as far away, the plant under it gets 1/4 the light. House light 4' or more from the plants does nothing.

Some plants will do all right on a window sill, especially if it is a south facing good sunny window sill. Some need more than that. Many of us who start a lot of things from seed use fluorescent tubes hung so they are just a few inches from the plants.
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To elaborate a little bit more on the lights some of us use; they are the fluorescent kind with the long tubes. There are a few different styles, but most people tend to go with the T8 variety, which is about 4ft. long, uses 2 bulbs, and can be bought for less than $15 at a Lowes or WalMart. The bulbs you use in it should be 6500K bulbs; this refers to the light spectrum the bulbs produce light in. The "cool" spectrum is good for growing plants indoors to be transplanted outside later.

You may also want to get a $5 outlet timer and use it to keep the light on for about 16 hours per day during the standard daylight hours.

Hope this helps some :).
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Timlin
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Over the years I've done both. I enjoyed growing under lights where the seedlings were right nearby and I could watch their development but a few years ago I had a greenhouse built for me and it has a heater in it so I can trust it on cold nights. I miss the seedlings in the house although I don't miss the mess and the crowding in the last few weeks before planting out.

With the greenhouse you often have to have heat for cold nights and you have to be around during the day to see things don't overheat in the sun. Those problems don't come up when your doing it in the house under lights.

TZ -OH6
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Even though out last frost date here is in late May we often have long periods of sunny warm weather and I don't hesitate to put the seedlings out on the east facing side of the house during the day as long as the morning temps are above 50. They come in at night so that the roots don't get cold.

tedln
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I sprouted and grew my tomato seedlings this year under a regular incandescent light. I did have it about eighteen inches about the seedlings. I also noticed they didn't develop the deep rich green color seedlings develop under the proper fluorescent "grow" lights. They did develop the green color after I moved them into the sunlight after a few days.

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rainbowgardener
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Yeah, the trouble with incandescents is they give off so much heat. You couldn't put it any closer to the plants, it would cook them. If my fluorescents were 18" above the plants, the plants likely wouldn't be as green either.
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TZ -OH6
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Remember back in the days of cameras that used film? If you didn't use special tungsten film when shooting indoors the pictures looked yellow? That's because incandescent bulbs have very little blue light, which plants need. So incandescents tend to starve plants. Fluorescents put out mostly red, green and blue light, and becuse of the low heat you can get them closer. Special plant fluorescents cut down on the relative amount amount of green, and are not really needed/economical for short term seed starting.

garden5
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TZ -OH6 wrote:Remember back in the days of cameras that used film? If you didn't use special tungsten film when shooting indoors the pictures looked yellow? That's because incandescent bulbs have very little blue light, which plants need. So incandescents tend to starve plants. Fluorescents put out mostly red, green and blue light, and becuse of the low heat you can get them closer. Special plant fluorescents cut down on the relative amount amount of green, and are not really needed/economical for short term seed starting.
If you've ever turned on an incandescent light during the day, you can really see the orange/yellow hue it gives off. Aside from not having enough light in the preferred spectrum, they also have to kept so far away due to their heat output that it wouldn't do any good even if they had the right spectrum. I also agree about the MH and HPS lights being over-kill for an average home gardener.
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TZ -OH6
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Yes MH and HPS are over kill, but I was thinking about some of the specialty fluorescents. The GE plant and Aquarium tubes are not that expensive and often sold at Lowes/Home Depot, but there are some things like VitaLites and salt water aquarium lights that are really expensive. Some of these are actually for reptiles but I've seen gardners recommend them. I wouldn't use either for seedlings because I might need to use that shoplight for human use at some point during the other 10 months of the year.

The cheapest fluorescents are the industrial warm whites and cool whites, which are lower quality for plant growth. They work but they are wasting energy by making a ton of green light plant can't see.

All of the next step up fluorescents cost about the same and usually have daylight in the name, but the color temperature indicates how much blue is put out, high numbers (5,000K, 6,000K etc) are better. Think white hot temperature vs red hot.

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I throw cheap compact fluorescents (spiral screw-in bulbs) over my plants and also toss them in a window.

I consider it supplemental lighting, and do use a timer. The plants do grow towards the bulbs til the sun hits them, so there's plenty of lumens there to aid in growth.

I hang them from pendant sockets, with a PVC frame...very unsightly but effective and cheap :)

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Can someone show me picture of one these shoplight T8 do hickeys? I have generally found if I walk into one of big chain stores and ask for something specific like that they look at me like I'm insane and 7 people later I MIGHT have what I'm after.......

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rainbowgardener
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Shop light is just your basic fixture to hold fluorescent light tubes. I guarantee you they will know what you mean. Looks like the $19 one here:

https://electrical.hardwarestore.com/13-38-shop-lights.aspx

T8 is just the size bulbs that are standard for them. They used to be standard for T12's, which are the older, fatter tubes. The last time I went looking, earlier this year, I couldn't find fixtures for T12's (though they were still selling the tubes), everything had gone to T8's. They are skinnier tubes, but brighter lights.
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TZ -OH6
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https://www.northerntool.com/images/product/images/900508_lg.jpg

Shoplight fixtures will be in a box approx. 4 ft long 8 inches wide and three inches deep. On the box there will be somplace that says either T-12 or T-8.

There should be a pile of tubes some place close by and on one of the ends will be printed the name, some code numbers, T-7 or T-12, and the color temperature (5,000K etc.)

T-12 = 1 inch tube diameter, T-8 = 8/12" = 2/3 inch diameter.



You don't have to hang the fixture, I put boxes under each end to hold it over the plants. Putting reflective "walls" around it (but not over it) will boost the light hitting the plants . Aluminum foil is 80-88% reflective so is useful for this by itself or taped onto cardboard etc. If using in front of a window be carefull about backing the plants because of heat build up.

Dixana
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Gosh you guys are beyond awesome :D
So since your so good at explaining everything ;) can someone give a run through of the differences of the light output blue, red ,etc and which is best for which plants? I hope everyone gets what I'm asking....

TZ -OH6
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The chlorophyll molecules of all plants absorb both red and blue light, but reflect green and yellow. Blue light has more energy so is more important for growth. Red light is needed to induce flowering, and plants grown under red shifted light such as high pressure sodium plant lights, tend to be undesirably lanky. Plants grown under blue shifted Metal Halide plant lights grow well, but don't like to flower. Seedlings don't need to flower so more blue light is better for their growth.

The human eye has three color receptors, red, green and blue (look closely at the pixels on your TV set, every color we see is a result of mixing red green and blue). Human ancestors evolved in a plant-filled green world so our eyes are sensitive to green light. Fluorescent lights put out white light as a function of three main phosphors making up the white powder coating the glass. The phosphors fluoresce red, green or blue light, but are heaviest on green to look brighter to people.

Cheap cool white tubes have alot of green and look white, or "cooler" than warm whites, cheap "warm white" tubes have alot of red and look "warmer". Color temperature is different, it represents the spectrum put out by an incandescent filament at a given temperature in degrees Kelvin. Hotter temperatures produce more energetic colors, red light is low temp low energy, blue is high temp high energy (red hot vs white hot). This output is a continuous spectrum like a rainbow (ROYGBIV). Fluorescent lights cannot put out a continuous spectrum because the light comes from the inidvidual colors that each phosphor produces, so imagine a rainbow that is black except for the very middle color of red green and blue (no orange, yellow, green-blue etc).

There is alot of word play when fluorescents advertize "full spectrum", and "Daylight". "Full spectrum" means that they have some additional phosphors besides red green and blue, such as yellow and orange (but the spectrum still looks like a black rainbow with some color stripes).

"Daylight" means that they fool the eye into seeing colors similar to daylight hitting the object instead of the icky greenish light of industrial cool white tubes.

Back to color temperatures... 4000K "daylight" tubes look like "warm white" tubes. The low temperature indicates a lot of red light compared to blue light. 6,500K "daylight" have alot of blue, and look whiter (I once bought one that said "arctic" daylight --not good for a homey feeling kitchen).


The new ultra energy efficient LED plant lights only have red and blue lights (and make plants look purple). Fluorescent plant lights have reduced green so they look pinkish, some used to have much less green but people didn't like them.



This site has some images of spectra for sun, plant absorption and fluourescent lights.

https://generalhorticulture.tamu.edu/lectsupl/Physiol/physiol.html

Dixana
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:shock: Wow thats a lot to take in! But I finally got what I needed tio understand! 6500k is what I need for seedlings cuz they have more blue light!! Sorry I have to be so pesty and understand the "why" of everything. Thanks again guys!

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