The Cannabis Grower’s Guide To LED Grow Light Coverage

LED Grow Light Coverage

Over the last few months, it has become blatantly clear that the primary reason people are purchasing LED grow lights is NOT to grow tomatoes and herbs.  While I am sure there are a select few visitors that do actually grow everyday food or herbs indoors and even fewer still that inquire about outfitting a greenhouse for any number of plants, a majority of site visitors are here for one reason: using LED grow lights to grow cannabis.

Dear Feds,

Neither myself or this website condones or supports any illegal activities.  Information is provided for legal medical marijuana growing operations and educational purposes in the event laws change.  All readers are expected to check with local laws before growing.

With that out of the way, it is safe to say that most of this site's visitors that purchase LED grow lights are doing so with the sole purpose of growing cannabis for personal/medical use.  I know this and, most importantly, LED grow light manufacturers know this as well so why do most of the published coverage areas seem out of touch with reality?

LED Grow Light Coverage

While some grow light companies flat out overstate their recommended growing area simply to dazzle the visitor into purchasing, others have not-so-sinister reasons for their claims.  The former is out to make a quick buck - customers be damned - and they end up shooting the industry in the foot by perpetuating negative reviews.  This is especially true of low-wattage LED panels and spotlights (LED grow panel review). The latter is trying (sometimes to the detriment of its bottom line) to keep neutral by not catering to any particular customer niche, i.e. Cannabis Growers.

Coverage area varies widely depending upon many factors:

  • manufacturer
  • wattage of individual diodes
  • shape of the grow light
  • degree angle of the diodes
  • overall wattage of the light
  • intended usage
  • . . .  the list goes on

Of all of the reasons coverage is affected, the most important is its intended usage.  You see, many manufacturers publish coverage areas based on the vegetative stage.  This is a very important point.  When plants are in the vegetative stage, they need less intense lighting than in the flowering stage.  As cannabis growers already know, getting plants successfully through the vegetative stage with LED grow lights is pretty straight forward at this point.  It gets tricky when bringing your plants through the flowering stage successfully due partly to the fact that some lights are just not up to the challenge.  More importantly manufacturers are eager to show clients a huge savings in electricity (thus justifying the higher entry cost) stating a 90W LED grow light can support a gardening space of 4'x4'.

Let me be blunt here - a 90W LED grow light CAN support a 4'x4' footprint but only during the vegetative growth of plants like lettuce, herbs, and some fruits and vegetables.  If that is what you are wanting to grow then you will do just fine.  For those of you growing cannabis, coverage expectations need to be put in check.

Big Grow Space - Little Light, A Recipe For Disaster

A common complaint about LED grow lights among cannabis growers is that they just don't get the yield they were expecting as compared to their previous grows using HID lights.  Or things might look great when growing - big leaves, tons of buds - but comes up short on dry weight due to light, airy buds instead of the thick, dense buds they may be used to.

If your buds are looking like the wispy little nug on the right, then your issue could be that you are trying to grow more than your light can handle.  Trying to force that 90W LED grow light to fully flower all your plants in a 4'x4' space is never going to work.

What you need to do is reduce the coverage area - generally by 50% - of what a manufacturer states the light can handle for the common gardener growing flowers or herbs for cooking.  So now you can use that 90W LED grow light in a 2'x2' space (enough for a couple decent plants or even a SOG/SCROG) and come away with thick, dense bud as you see in the picture below on the left.

LED Grow Light Coverage Area Guide

I have already stated that there are many factors that can affect the coverage area of LED grow lights, here is a rough guide to what I think are suitable grow spaces for a given wattage of light. There are many LED manufacturers and many more wattages of lights so here is a list of common sizes. All lights listed are tri-band, 5 spectrum grow lights. By keeping these guidelines in mind with your growing effort, you will find that your results will match or exceed your expectations.

Light Wattage Vegetative Stage Coverage Flowering Stage Coverage
90 Watt 4' by 4' 2' by 2'
180W 5' by 5' 3' by 3'
350W 6' by 6' 4' by 4'

{ 215 comments… read them below or add one }

TL April 7, 2012 at 10:49 am

I have a 3 x 8 with about 5 1/2 ft in height room……inheriting a plant that is already been veging and is about 12in tall already ……. Should I continue to veg when I get it or when is it ready to switch to flower and what wattage should I use …… Appreciate your help

DAVID S NEWSOME April 16, 2012 at 5:42 pm

I AM A COLLAGE STUDENT MAJORING IN HORTICULTURE AND EXPREMENTING GROWING THE CROCUS STAIVUS L. PLANT INDOORS UNDER LED LIGHTING . HABIT OF PLANT : FLOWER IN FALL 12 “+-TALL / GRASS LEAF GROWTH IN SPRING 16 TO 24″ TALL/ DIE BACK GRASS SUMMER / FLOWERS AGAIN FALL . TEST BEDs WILL BE 3- 3′x 3′ AREAS. I HAVE BEED LOOKING AT (3) 90 WATT TRI BAND 1 FOR EACH BED IS THIS ENOFFT LIGHT REQUIMENT OR WHAT ARE MY OPTIONS ..? NOT SURE ANY SUGGESTION? BEING A STUDENT DO YOU OFFER ANY DISCOUNTS? THANKS

HydroMan April 25, 2012 at 3:02 pm

Sounds about right – check with the guys at ProsourceWorldwide.com . . . they are good with this kind of thing.
Hydroman

HydroMan April 25, 2012 at 3:19 pm

rStyle –

You would need no less than 9 180W lights (up to 25) to fully cover 3×3 meters.

Hydroman

tyler February 12, 2013 at 8:18 am

hey guys i need a little advice im looking to start just one indoor soil plant under led lights my grow space is 3′L 3′W and 5′H i want to do led but i need to know a good grow light that i can use and what wattage i should use for only one plant and thats not to expensive also what a good quality type of nutriens anyone can recommend

mandy April 1, 2013 at 10:06 am

I have a 80x80x160 grow tent, i intend to grow 3 drawf auto flowering plants, not sure what wattage etc led lights i would need

HydroMan April 1, 2013 at 10:18 am

Mandy –

I would look for something in the 200-250w range. A great company that I have been working with for a while on testing is http://www.truliteled.com . . . right now they say on their site that they are selling to wholesale accounts only but just give them a call, they can help you out.

Cheers!

mandy April 2, 2013 at 1:41 pm

Thanks for your help, i was thinking 150w so glad i checked

HydroMan April 2, 2013 at 2:38 pm

No problem!

ralph April 30, 2013 at 3:32 pm

whats your opinion of the advanced led 600 watt light, its also being marketed by another company called diamond. these lights look well made and have 300 3 watt led’s but the manufacturer claims they run the led’s at 2/3 their power level which makes a 600 watt light. they also have the x-lens and 60 degree primary, 90 secondary angles and 11 wave lengths. I am planning my first garden and will have 16 plants on each side but want the most efficient technology I can get so I’m exploring all my options . . .

HydroMan April 30, 2013 at 3:38 pm

Hey Ralph –

I am personally not a fan of Advanced . . . too many wavelengths, not enough research done to dial them in. After all my testing, I have been sticking with http://www.TruLiteLED.com . They give very accurate wattage on their lights – no games. To put it into perspective, their 400W light uses 336 x 3w diodes . . . some companies would call this a 1000w+ light! Their lights are based on 5 wavelengths – very precise and targeted.

Give them a call, they will get you set up!
Cheers!
Hydroman

smege July 30, 2013 at 4:08 pm

i have a grow tent that’s about 2.4 meter x2.4 x2.4 and an apollo18 LED i was thinking of using a light rail to move the LED panel do you think this is a viable method as this will be the first time i will be using LED’s

HydroMan July 31, 2013 at 9:25 am

Smege –

That panel should be able to cover about a 2×6 for flowering. Putting it on a light rail could boost that to about 3×6 but that leaves more than half your tent uncovered.

Bottom line is – you need more light! Check out TruLiteLED.com…

Later,
Hydroman

playaboyy02 August 11, 2013 at 11:02 pm

Right now I am planning on a sog in a 4×4. I have 50 clones that are almost done rooting and will be put into veg for 10 days then into flowing. I have a 240w blackstar led in there right floweing the 4 mothers I didn’t want to keep. Will the 240w led be enough for 50 plants? I have an extra 240w led that I can use for a total of 480w of led light plus a 25w fluro uvb. Do you think I need the extra 240w led in there? TIA.

HydroMan August 13, 2013 at 10:19 am

PlayaBoyy02 –

Absolutely – put in the other light. I would normally put 400-600W of LED in a 4×4 to match or outperform a 1000W HPS.

Later!
~Hydroman

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