Plant Light Recommendations 2020

Plant Light Recommendations 2020


Was the distance between the lamps and plants,done by your own experimentation?
I have two Citrus,about a couple years old,under a bank of six T5 tubes.There is information that varies in how close to get.One plant seems to really like it a few inches from the canopy and is putting on new growth.
These aren’t new starts,but in your opinion,is there an ideal range?bb

The distance was determined by measuring the PAR flux at one meter from the source and then calculating the distance to achieve 125 PAR W/m^2. The distance can vary significantly with manufacturer – even for sources of the same listed specs.

The link to the spreadsheet at the bottom of the list contains the calculations.

Here’s photos of the 4’ Active Grow system measurements.

Thanks very much,Richard.I’ll look into getting a light meter and do some

So 20,000 lumens 5" above the plants is too much?

I’m glad this thread is here because if it wasn’t, I’d start one!

My question is about the difference between “tube” LED lights (that look like standard shop lights) and the ones that Richard posted, with the grids of tiny bulbs.

I’ve had a couple “grid bulb” lights for a few years and just bought a couple fluorescent tube types and I’m trying to understand the difference in the lights and the different spacing required.

My “grid bulb” lights say the following:
Power: 300W
Color: 9 band
Led Qty: 100 PCS*3W

My “tube bulb” says:
42 Watts
4000 Lumens
4000K color temp

I don’t know what I’m supposed to make of any of that since the only units that are the same are the watts!! I’m guessing the 42W bulb can be much, much closer than the 300W light, but I really don’t know. Which of those different “ratings” should I be concerned about?

Also, not having a light meter, is there any way to calculate proper distance from plants?


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@Chikn -
Lumens should never be mentioned in a discussion of plant lights – except perhaps to point out that they are listed on the packaging due to an architectural labeling law. Despite misleading claims of marketers they have no application to horticulture.

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@Bart -
The wattage listed on plant lights and LED lights in general can be misleading. Sometimes they refer to incandescent equivalent and other times to actual maximum power draw.

The industry refers to “grid” lights as Integrated LED. The elements are machine manufactured in large sheets. They are essentially throw away systems once the elements are past useful output. For indoor commercial lighting (e.g. office, warehouse) this can be a decade. For plants though, about 4 years.

Your LED tube lights contain a strip of grid lights. LED tubes for commercial use are glazed on the outside while those assembled for plants are clear on the “front” half and reflective on the back half. The former are mass-produced and a fraction of the cost. However the clear lights are twice as efficient in delivering light to plants. One supplier of the latter is Active Grow. I’ve attached a photo of their bulbs.

Without a meter that measures PPFD it’s difficult to estimate height. What systems do you have?


Thanks Richard!

My “shop lights/tube lights” do indeed say "integrated LED tubes on them, so one mystery is solved!

My older lights (300W listed above) are: Roleadro Plant Grow Light, 600W LED Grow Light Full Spectrum Plant Light Dual-Chip Growing Lamp with ON/Off Switch,Daisy Chain for Hydroponic Indoor Plants Veg and Flower (only 110V) Here’s the Amazon link to them:

The Roleadro lights above seem pretty powerful. At 3 feet or so of distance, certain plants show some burning.

The ones I called the shop light/tube light were a Costco special. There’s not much info on the box other than what I already listed above. They are by Feit Electric. I can send a photo of the box if that will help. The model number is listed as Shop/840/LED


It looks like your PAR meter is the one from Hydrofarm.By reading some reviews,the new models seem accurate enough,but they may have the design flaw,with the wires either pulling loose or shorting by touching.Some people add hot glue at the terminals,to stabilize the looseness.
Did your unit ever freeze up or malfunction,because of that problem?bb

@Bradybb -
I haven’t had trouble with the unit. What light system do you have? Perhaps I can do the calculation here.

@Bart -
I’ll check on those and get back to you.

Thanks,that will save me an expense,if possible.
There are 6 of these with a reflector hood.

AgroMax 4 Foot (45.75") 6,400K Grow T5 Fluorescent Grow Light Bulbs - F54T5HO Bulbs

@Bart -
Your Roleadro 600W equivalent is a bit of a puzzle. It’s rated 165W power draw but a small portion is for the fan. It uses blurple elements which deliver less PAR Watts than the latest elements but it has 60° cones which create greater light intensity under the fixture than those without.

My estimate isn’t much help: 20" with an error margin of +/- 8".

For the purposes stated in my document linked above, the color spectrum of this system is not a great choice.

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@Chikn -
What kind of system do you have?

If mine isn’t available to calculate,because of the fluorescent tubes,I also have this model.It’s being used indoors,in a small grow tent,for younger tropical and subtropical plants.

VIPARSPECTRA UL Certified 450W LED Grow Light, with Daisy Chain,Veg and Bloom Switches, Full Spectrum Plant Growing Lights for Indoor Plants Veg and Flower

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About 14.4 inches.

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These, with 2 bulbs?’-linkable-led-shop-light%2C-2-pack.product.100462723.html

Hey,that’s great.Very precise.Thanks

This is all Greek to me. I just go by if the plants seem to be flourishing.

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@northwoodswis4 -
Check the document linked in the first post.