Tomatoville® Gardening Forums - View Single Post - LIGHTS

saucy boy · April 3, 2018

Hi, folks. I'm not sure if this my first post on this forum, but if not it's been a while. 😉Thought I'd chime in on a few things here and there.

I grow my tomato starts in 72 cell plug trays. I use two 8-bulb 6300K T5HO fixtures to cover 9 trays. They give off a lot of heat, so much that don't need germination mats to get the soil up to 85°. I can even put 4 trays on top of each fixture and get the soil up to around 80°, which allows me to use my mats for other starts.

I used a photographic light meter to see how much light falloff I get as the fixtures are raised. In theory, the light intensity should get four times as bright for every halving of the distance, but in the real world the light intensity stops increasing at distances any closer than about 6".

At 6" distance these fixtures give off the same amount of light as we get here (Upstate NY) in our nursery at midday on an overcast day. In full sun the light intensity is over 2 "stops" brighter, which is more than 4 times as much light energy.

Under my lights the air temps can get over 100°F if they are too close. The lights won't "burn" the leaves, but the air temp is way too high for best growth, and the trays dry out and need constant watering through the day. So I aim for about 8" minimum distance once the seedlings emerge, as it is enough light for adequate growth, but not so close as to cause heat buildup problems.

Sorry if my first post seems a bit wordy, just trying to share what I've discovered.

April 3, 2018	#25
saucy boy Tomatovillian™ Join Date: Jul 2014 Location: Upstate New York Posts: 4	Hi, folks. I'm not sure if this my first post on this forum, but if not it's been a while. 😉Thought I'd chime in on a few things here and there. I grow my tomato starts in 72 cell plug trays. I use two 8-bulb 6300K T5HO fixtures to cover 9 trays. They give off a lot of heat, so much that don't need germination mats to get the soil up to 85°. I can even put 4 trays on top of each fixture and get the soil up to around 80°, which allows me to use my mats for other starts. I used a photographic light meter to see how much light falloff I get as the fixtures are raised. In theory, the light intensity should get four times as bright for every halving of the distance, but in the real world the light intensity stops increasing at distances any closer than about 6". At 6" distance these fixtures give off the same amount of light as we get here (Upstate NY) in our nursery at midday on an overcast day. In full sun the light intensity is over 2 "stops" brighter, which is more than 4 times as much light energy. Under my lights the air temps can get over 100°F if they are too close. The lights won't "burn" the leaves, but the air temp is way too high for best growth, and the trays dry out and need constant watering through the day. So I aim for about 8" minimum distance once the seedlings emerge, as it is enough light for adequate growth, but not so close as to cause heat buildup problems. Sorry if my first post seems a bit wordy, just trying to share what I've discovered.