Led for close canopy operation

I’m looking to build a lettuce grow rack. I’m looking for a alternative to going with T5 HO lights.

I want to do a 3 or 4 level rack. So lights will be close like 6”.
What’s out their.

T5 HO lights LOL

Herb & Suds said:

T5 HO lights LOL

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I kinda feel like the T5 is the best bet. But I thought maybe be something out their to compete

Bookush34 said:

I kinda feel like the T5 is the best bet. But I thought maybe be something out their to compete

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It still remains many greenhouse owners go to

Bookush34 said:

I’m looking to build a lettuce grow rack. I’m looking for a alternative to going with T5 HO lights.

I want to do a 3 or 4 level rack. So lights will be close like 6”.
What’s out their.

Click to expand...

Can look at the 48" GE grow strips on Amazon.....DIY would open more options, better performance for the$

PSUAGRO. said:

Can look at the 48" GE grow strips on Amazon.....DIY would open more options, better performance for the$

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Are you familiar with growing lettuce ?
Because I have no clue how much light is required

Herb & Suds said:

Are you familiar with growing lettuce ?
Because I have no clue how much light is required

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Not indoors under artificial lighting

Our resident lettuce "expert" could answer that..... Tagging @OneHitDone

Herb & Suds said:

Are you familiar with growing lettuce ?
Because I have no clue how much light is required

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I found they like 300-350 PPFD.
DLI of 15-20
And temps under 70F for tight heads and sweet tasting leaves.

Having a hard time finding PPFD charts for T5 HO. But lettuce doesn’t need tons of light.

Bookush34 said:

I found they like 300-350 PPFD.
DLI of 15-20
And temps under 70F for tight heads and sweet tasting leaves.

Having a hard time finding PPFD charts for T5 HO. But lettuce doesn’t need tons of light.

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I'm thinking he is talking leaf lettuce not heads at 6 inches clearance

Herb & Suds said:

I'm thinking he is talking leaf lettuce not heads at 6 inches clearance

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I mean loose leaf and heads.
I have done it with my cobs dimmed down. But you still need lots of head room.
With my vero29s 400watts. I bet you I could grow lettuce in a 6x6 with the light 60” above the plants.

Bookush34 said:

I mean loose leaf and heads.
I have done it with my cobs dimmed down. But you still need lots of head room.
With my vero29s 400watts. I bet you I could grow lettuce in a 6x6 with the light 60” above the plants.

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I understand but he wants to grow shelves of lettuce like starter trays with six inches between shelves

Herb & Suds said:

I understand but he wants to grow shelves of lettuce like starter trays with six inches between shelves

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I am the OP.
Not 6” between shelves. But the light within 6” of the plants.
The shelf would probably be 24”.
4” of light and 6” of pot.

I’ll be able to grow 8-10” tall plants max.

@Bookush34 , not sure if you have seen my lettuce thread but you may find some helpful info there.


As for light levels, I have done best at 250ppf + if your looking for big plants with leafs you can actually use to make lettuce wraps etc.

Now I will speak on lights I have used first hand on lettuce.
T5 HO - The Gold Standard and does a phenomenal job growing lettuce to full term.
Metal Halide - does a fantastic job but I prefer the T5 on young sprouts
HLG QB96 4K - tight bonsai heads that grow very unnatural in structure and the light has to be placed high in the stratosphere
HydroGrow RGB old school led's - did better than the HLG QB65 but not as good as MH or T5 with slightly elongated leaves
Vero18 4K cobs - similar to HLG65 4K

Now that I have made it pretty clear that T5 is my first choice there are some options.
I have tried the Philips Direct Replacement T5 LED tubes you can get at Home Depot in 4K. The do match very closely an HOT5 in par output and the growth under them was surprisingly good at 25w per tube
This is what the Philips lamps look like. Heavily frosted.



The Next option in the T5 realm I came across that I actually invested in and tried are the 4K direct replacement tubes by Bios.


Immediate response with installing these and putting the par meter under them was "Holy Shit". These bad boys are putting out about 100 more ppfd at 12" from the fixture than traditional T5 HO at only 25W per tube!
Only downside to these (not really a downside) is that they are glass and UPS has a thing for breaking them in shipping.
Note that with the philips lamps above virtually no light was hitting the reflector. The Bios tubes do hit the reflector with the open glass design and it really scatters the light and throws it everywhere for a more even coverage



The Growth under the Bios tubes so far has been very impressive. and I would highly recommend them to anyone who already has T5 fixtures and interested in a retrofit.

If someone does not have T5 fixtures already I would probably be looking at these Bios LLi fixtures for leafy greens


Now, why does one 4K led product grow greens very well and the next product not so much? That seems to be the million $ question and where the mystery lies. Another forum member and myself have come to the controversial conclusion that plants just do not like bare diodes (think laser beam).
Putting a piece of glass in front of the diode or even a conformal coating seem to be enough "diffusion" to soften the blow of the plant seeing the diode head on. We have done many tests and cannabis in particular will take super high ppfd levels beyond 1200ppfd if the light is diffused in this manner while developing serious plant health issues at the same light levels under bare diodes of the same spectrum.
Why some light makers continue down the bare diode path is beyond me at this point. On top of the above mentioned functionality issue there is also the issue of durability exposing microelectronics to grow room conditions and making it very difficult to clean the led's.

Anyways, hope this helps in your choice of lighting for your lettuce project

Bookush34 said:

I am the OP.
Not 6” between shelves. But the light within 6” of the plants.
The shelf would probably be 24”.
4” of light and 6” of pot.

I’ll be able to grow 8-10” tall plants max.

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Ah, I misunderstood you as well.... Thought seedlings.

Can look at nextlight veg8 for a 2x4 t5 ho swap.

Edit. What OHD said as well..... Retrofit led bulbs are a good option

Bookush34 said:

I am the OP.
Not 6” between shelves. But the light within 6” of the plants.
The shelf would probably be 24”.
4” of light and 6” of pot.

I’ll be able to grow 8-10” tall plants max.

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That much space makes a big difference , my bad