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Old 03-13-2013, 12:08 PM
 
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Default Grow Light on 24/7 or No?

Hi group,

I'm growing some veggies from seed this year and installed a 1000-watt grow light, which currently hangs about 4 feet over the seedlings. They are situated in my basement next to a window.

My question is this: should I leave the grow light on 24 hours a day, even during daylight hours, or should I turn it off during the day? They do get sunlight during the day, but certainly not as much as if they were on my main living floor (but that won't work logistically, so the basement it is).

Another idea is to simply move the seedlings outdoors during the day to get natural sunlight. Or do they need the concentrated light from the grow light 24 hours?

Thanks for any tips.
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Old 03-13-2013, 01:48 PM
 
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Leave the lights on during the day and off at night. I give mine about 16-18 hours of light. They should get used to what their natural conditions will be.

You can also move them outdoors during the day to a protected area, as long as you're not expecting flooding rains, high heat or intense sunlight. As bright as your artificial lights might seem, nothing is as intense as the sun. Young plants can get sunburned very easily. Bring them out foa few hours at first and increase the time as they become acclimated.

Having said that, I've always found it to be a real pain to keep moving them, LOL!
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Old 03-13-2013, 02:32 PM
 
Location: Under the Redwoods
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Vegetables need light to tell them what to do, when to flower and such. They should not have full time light for too long. While they are seedlings, 24 hours of light will not hurt them, it helps them to establish a good root system and they will not get too tall too fast which can weaken the plant.
I assume that you will be transplanting the seedlings outdoors? You will want to take some time to acclimate them to the 'weather' and light changes if you do. And do not be surprised if the plants 'freak out' when you transplant them. They may go into shock, but with care they will come back just fine.
If you plan on keeping them indoors for the whole season, turn the light off after 18 hours. Then when it comes time to flower and fruit, cut back to 12 hours of light.
This is what is most natural for the plants.
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Old 03-15-2013, 11:49 AM
 
Location: Michigan
2,115 posts, read 889,585 times
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I go about 18/6 or 16/8 when germinating seeds since the lights provide warmth, and I've read some studies that suggested that some temperature fluctuation is often beneficial to germination as opposed to a constant temperature 24 hours a day. In some plants more than others, but one of the studies was done with capsicum (peppers) which I grow the most plants of. A lot of my others plants are also nightshades (tomatoes, eggplant, and tomatillos) so it's likely to be the same for them.

Plants in vegetative growth don't need darkness though. They will not be harmed by 24-hour light as a general rule, though there are probably some exceptions (onions will bulb too early with too much light). I do believe there are diminishing returns after ~16-18 hours of light a day though. So the question is, is any extra growth from leaving the lights on 24/7 worth the extra electricity? Running a 1,000 Watt light 24/7 uses a lot of electricity. 1,000 Watts= 1 KW. At a price of $.12/KWH comes out to $86 per month. At 16 hours a day that's $57 a month.

I'm going assume your 1,000 Watt light is an HID lamp, either metal halide or high pressure sodium. These should not be left on constantly for long periods of time. Manufacturers recommend that you turn these lights off for 15 minutes every 24 hours. If you don't you might have a bulb explode. These lamps are not cheap and picking glass shards out of potting mix is not a whole lot of fun, so you should at least turn them off for 15 minutes per day.
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