Most people buy a bigger light than their tent needs, hang it high, and pay every day for light that lands on the walls. We would rather sell the right one. Compare LED grow lights on 2 numbers, not watts.
The 2 numbers that matter
- µmol/J (efficacy). Light per joule of power. Look for 2.5 or better; 3.0 is top tier. A 2.7 µmol/J light at 400W out-performs a 1.7 µmol/J light at 600W and costs a third less to run.
- PPFD. Light landing on the canopy. Aim for 200 to 400 for seedlings, 400 to 600 for leafy growth and 700 to 1,000 for fruiting plants like tomatoes and chillies. Check it with a PAR meter.
Sizing watts to your tent
Rule of thumb: 400 to 450W of modern LED per square metre for flowering. A slightly bigger light dimmed down is fine. A 1.5m light over a 1.2m tent is not.
| Tent | LED watts (flowering) | Picks from the shelf |
|---|---|---|
| 60 x 60cm | 100 to 150W | Cultiv8 UFO 100W (2.5 µmol/J), Hortitek Gen 2 UFO 200W (dimmed) |
| 80 x 80cm | 200 to 250W | Hortitek Gen 2 Growboard 220W (2.5 µmol/J), Ulight ECO 360W (2.7 µmol/J, dimmed) |
| 1.0 x 1.0m | 300 to 400W | Digi Lumen Extreme 400W (3.0 µmol/J), Treegers GL300W (made for 1.0 x 1.0m) |
| 1.2 x 1.2m | 450 to 650W | Lumatek Zeus Pro 465W (2.7 µmol/J), Treegers GL420W (made for 1.2 x 1.2m) |
| 1.5 x 1.5m | 650 to 800W | Lumatek Zeus 600W Pro 3.1 (3.1 µmol/J), Digi Lumen Halo 780W (2.7 µmol/J) |
| 2.4 x 1.2m | 800 to 1,000W | Digi Lumen Extreme 1000W XL (3.0 µmol/J), Lumatek Zeus 1000W Pro Evo 3.1 (3.1 µmol/J) |
Every watt becomes heat, so size the light with your grow tent and inline fan and carbon filter. More in our LED buying guide.
LED grow light questions
How many watts of LED do I need for a 1.2 x 1.2m tent?
About 450 to 650W of modern LED for flowering and fruiting plants. The Lumatek Zeus Pro 465W and Treegers GL420W are both rated for a 1.2 x 1.2m footprint. A 720W fixture like the Digi Lumen Extreme 720W also works if you dim it. Compare µmol/J before you compare watts.
What does µmol/J mean on a grow light?
It is efficacy: micromoles of usable light per joule of electricity. The higher it is, the more light you get for the same power bill. Look for 2.5 µmol/J or better. 3.0 µmol/J and above is top tier.
Is a more expensive LED always better?
No. 2 fixtures with the same diodes and driver class perform almost the same whatever the badge says. Pay for efficacy, driver quality, cooling, even spread and a warranty someone will honour. Do not pay $500 extra for a brand at the same µmol/J.
How high should I hang my LED grow light?
At the height the maker states for your fixture, then dim it if the plants need less. Do not buy an oversized light and hang it high to compensate. That gives a hot spot in the middle, weak corners and wasted power. Check the result at the canopy with a PAR meter.
