Grow Lights

[Plantersville]

Just wondering what some of you do with grow lights. Do you leave them on 24 hrs a day or just like leave the on for about 20 hours or 12 hours per day?
Thanks for any input!

[Gobig_or_Gohome_toms]

I set them on a timer for about 16 hours a day. Give them them night time to do what is typically natural to them.

Craig

[Worth1]

16 hours a day
Worth

[Fusion_power]

You can leave plants under grow lights 24/7 but it actually suppresses growth. Plants need a photo period to accumulate sugars and a dark period to expend them in growing.

My light stand holds 36 fluorescent 4 ft bulbs and can accomodate up to 30 standard trays 11" X 22" at a time. I usually turn the lights on and leave them on for about a month when I start tomato seedlings. I have up to 60 trays of plants and every 12 hours I swap the 30 trays that are under the lights with the 30 trays that are sitting on top of the lights. There is a big reason for handling each tray this many times. It allows me to look at every cell and seedling to see what is going on with the plants and from holding the tray I can tell if water is needed. I can handle the plants this way and totally avoid over watering or under watering either of which can kill thousands of seedlings in a matter of hours.

Once the seedlings are about 4 inches tall, I move them to the greenhouse and transplant into individual trays of cells. This is a fairly efficent way to produce about 50,000 seedlings in a year.

DarJones

[Mike Maurer]

Originally Posted by Fusion_power

You can leave plants under grow lights 24/7 but it actually suppresses growth. Plants need a photo period to accumulate sugars and a dark period to expend them in growing.

My light stand holds 36 fluorescent 4 ft bulbs and can accomodate up to 30 standard trays 11" X 22" at a time. I usually turn the lights on and leave them on for about a month when I start tomato seedlings. I have up to 60 trays of plants and every 12 hours I swap the 30 trays that are under the lights with the 30 trays that are sitting on top of the lights. There is a big reason for handling each tray this many times. It allows me to look at every cell and seedling to see what is going on with the plants and from holding the tray I can tell if water is needed. I can handle the plants this way and totally avoid over watering or under watering either of which can kill thousands of seedlings in a matter of hours.

Once the seedlings are about 4 inches tall, I move them to the greenhouse and transplant into individual trays of cells. This is a fairly efficent way to produce about 50,000 seedlings in a year.

DarJones

I have looked for a reference to how long I should leave seedlings under the lights. You mentioned 4" and someone mentioned 2-3 weeks. How long is the recommended time?
Thanks, Mike

[Plantersville]

thanks folks for that helpful info..........

DarJones, good idea about putting trays above the lights........Im gonna try that!

[OtterJon]

I have mine (Ceramic Metal Halide 400w) on for 16hrs on/8hrs off seems to be about right.

Jon

[Hastings]

Can you use a full spectrum tube light? Or what works best to grow seedlings for artificial lighting, keeping cost in mind.

[bcday]

You can use a full spectrum tube if that's what you have. If you're buying new tubes and only using them for a few weeks to grow transplants, the cheaper cool white/warm white tubes work just as well. No need to buy pricey full spectrum tubes.

[tgplp]

This isn't scientifical or fancy but... I turn them on when I wake up and off when I go to sleep. plants do fine like that for me.

Taryn

[erlyberd]

I typically leave my cheapo, twin bulb, shop lights, with two cool white bulbs on for 8-10 hours a day and produce nice healthy seedlings. This is in a room that gets some natural light if it makes a difference. Also, I keep the bulbs 2-4" off the top of the plants. I normally grow my seedlings inside under these lights for 3-4 weeks and start moving them outdoors to gradually harden off.

[Skaggydog]

16 on 8 off to vegetate, 12 on 12 off to flower

[bobberman]

I got the best timer at Lowes that has 48 1/2 timers in it with 4 plugs. They were originally $12 and reduced to $9. I bought one and got it for $5. I liked it so much I went back and bought 2 more. I then decided to get two more and when I went backthey were reduced to $2.50 so I now have 8 total! Ican set a half hour for midnight and again 1 am and 2 am ect and its simple! Its mechinical just lift a tab. I set my fan in the greenhouse for noon 2 pm and 4 pm half hour each time! I can hook 4 plug or 4 fans! I even have a 200 watt mini heater set on one of the timers to heat for a half hour 4 times after midnight on cold nights!

[SEAMSFASTER]

I start my seedlings on a 2-tray Seedling Heat Mat with humidomes and blankets for extra insulation. As soon as the first seedling emerges, I transfer the tray to a custom-designed frame with two 40W T12 cool white bulbs set <2" above the top of the tray. I leave them there with lights on 24 hrs. per day until I estimate that at least 90% of the seedlings that will germinate have germinated.

During the very early phases, I've found it beneficial to have continuous light so that seedlings will have good light whatever time of day they decide to break the surface. This has really helped me to avoid growing pale, leggy seedlings.

Once I've completed the germination phase, I move the seedlings under 400W metal halide lights, which I have set on timers (of the type bobberman describes) for a 16/8 pattern. I use a fan to help strengthen stems. [The metal halide lights were rescued from the trash - too pricey for me to buy new.]

I recall reading somewhere that tomato seedlings can do fine with up to 20 hrs. of light per day, but really need that dark phase, as mentioned. In contrast, pepper seedlings do just as well without a dark phase.

As soon as outdoor temperatures get into the 50's I start hardening off, but I try (not always successfully) to not expose tomatoes and other heat-loving types to temperatures under 50°.

I agree that the cheapest tubular fluorescent lights can perform adequately if kept very near the surface of the tallest plants in a tray. Just today I purchased several more cheap-o fixtures for about $12 each, including the two bulbs!

A cost-benefit analysis just did not justify spending the extra $ for the more energy-efficient T5 bulbs. T5 bulbs cost >$8 each around here and the fixtures are about triple what I paid for the cheap-o T12 fixtures. It would take a decade or so to make up the difference in energy savings.

Metal Halide setup:

[amideutch]

This was taken out of the book "Greenhouse Tomatoes, Lettuce & Cucumbers" by S.H. Wittwer & S. Honma.


The tomato is a facultative short day plant which flowers and fruits earliest if the day is not extended beyond 12 hours by artificial light. Young tomato plants do not need the light intensities of full sunlight. Where there is no overlapping of leaves, light saturation is reached at intensities from 2000 to 3000 foot candles, or about one-fifth to one-third the intensity of direct sunlight at high noon. If artificial lights are used, an intensity of at least 500 foot candles should be provided at the leaf surface. Tests with fluorescent fixtures reveal that Wide Spectrum Gro Lux is slightly superior to cool white.
Hope this helps. Ami