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Question on light distance
- Thread starter Bigslimm
- Start date
Howdy...I use a SunBlaze T5 fixture, too. Good stuff!!
I know you're supposed to get as close as possible, but personally, I like a distance of 6 to 9", at least at first, for a few weeks after sprouting. Later, when the plants have a few sets of true leaves and are really taking off, I might take it down to 4-5". Even though T5's don't get as hot as T8's or T12's they still generate heat. The heat can dry out the plants pretty quickly and lead to problems if the light is too close. So, it can be helpful to start the lights further away from the plant tops and work your way down over time, erring on the side of not overheating the plants.
There is really no penalty for being conservative about it and not putting the lights too close; if the plants start getting too leggy you just lower the lights a little - it is not as easy to rectify the reverse situation of burned or dried out plants.
I wouldnt' set them more than 9 or 10 " away, though, because the amount of light received by the plants is an inverse square law type of deal - if the light's at 2" away and you move it to 4", the amount of photons reaching the leaves is 1/4th that of a 2" distance, and if you then move it to 8", the amount of photons received is 1/16th that of 2", and so on.
As SRB noted, you don't need light for germination. Only turn the lights on after you see some green. (I'm not even sure light is needed until true leaves - I've had seedlings get to that stage in complete darkness. I think the cotyledons are basically food sacks that get the plant all the way to first true leaves without any outside energy input. After true leaves appear, you definitely need light).
If (like most growers) you wanna keep the lights right on top of the plants at 4" (which I don't do), you'll probably want to get some small fans in there to circulate the air and blow off some of the heat. That'll really help a lot. Plus, it makes the plants grow stockier and tougher. In conjunction with the strong T5 lights, gently blowing fans virtually eliminate the need for tedious hardening-off when you take them outside - the seedlings are already used to "wind" and "sun" and are pretty much ready for life in the big city. In fact, after I got my T5s and fans, I stopped bothering with hardening-off. I just set them outside when it's time. They find real sun and normal daily winds easier to take than the torture of being baked under T5's and blown around with fans for eight weeks. They seem to relax and go into strong growth mode as soon as they get outside, with no hardening off.
I know you're supposed to get as close as possible, but personally, I like a distance of 6 to 9", at least at first, for a few weeks after sprouting. Later, when the plants have a few sets of true leaves and are really taking off, I might take it down to 4-5". Even though T5's don't get as hot as T8's or T12's they still generate heat. The heat can dry out the plants pretty quickly and lead to problems if the light is too close. So, it can be helpful to start the lights further away from the plant tops and work your way down over time, erring on the side of not overheating the plants.
There is really no penalty for being conservative about it and not putting the lights too close; if the plants start getting too leggy you just lower the lights a little - it is not as easy to rectify the reverse situation of burned or dried out plants.
I wouldnt' set them more than 9 or 10 " away, though, because the amount of light received by the plants is an inverse square law type of deal - if the light's at 2" away and you move it to 4", the amount of photons reaching the leaves is 1/4th that of a 2" distance, and if you then move it to 8", the amount of photons received is 1/16th that of 2", and so on.
As SRB noted, you don't need light for germination. Only turn the lights on after you see some green. (I'm not even sure light is needed until true leaves - I've had seedlings get to that stage in complete darkness. I think the cotyledons are basically food sacks that get the plant all the way to first true leaves without any outside energy input. After true leaves appear, you definitely need light).
If (like most growers) you wanna keep the lights right on top of the plants at 4" (which I don't do), you'll probably want to get some small fans in there to circulate the air and blow off some of the heat. That'll really help a lot. Plus, it makes the plants grow stockier and tougher. In conjunction with the strong T5 lights, gently blowing fans virtually eliminate the need for tedious hardening-off when you take them outside - the seedlings are already used to "wind" and "sun" and are pretty much ready for life in the big city. In fact, after I got my T5s and fans, I stopped bothering with hardening-off. I just set them outside when it's time. They find real sun and normal daily winds easier to take than the torture of being baked under T5's and blown around with fans for eight weeks. They seem to relax and go into strong growth mode as soon as they get outside, with no hardening off.
The T5 gets hotter than a t8 or t12 bulb all of my research confirms it in many many other posts on the web. this is y i chose a t12 daylight bulb 6500k 3250 lum they can be down to under and inch and even touch and not hurt the plant thats y i say with a t5 bulb be at least 4 inches 6 is prolly better...
here are a few quotes from other posts on the web
"You can only get about 6 to 8 inches from the plants with the t5 bulbs or you will burn them"
"My top shelve is t12 4 foot bulbs. Practically no heat compared to the t5 bulbs and I can let the plants grow right up to the light even touching them with no burn"
"Teamster's right though, they will get hotter than a t8 or t12"
"My second shelf has 4 t5 bulbs and it is hot but the third has 6 lamps and let me tell you that thing is hot. Burn to the touch"
i only opened my greenhouse lid once a day very quikly to wipe the moisture off this helps prevent fungus i wiped it same time everyday u can prop the lid when a few hook and take it off when the majority have hooked
good luck
I don't open the lid at all until I see some green - which is usually 5 or 6 days. After that, I give them 1 day with the lid ajar (like propped up with a toothpick in one corner), kind of a transition phase. Then I put the lid away until next year.
If you're growing mostly habs, it could take longer. That could look more like 10 or 14 days before you see green. Jalapenos, serranos, etc - capsicum annums - should be popping in 5 days or a week or so.
Basically, get the lid off as soon as possible once you see green, to avoid fungus.