You can buy a brilliant grow light and still get a poor grow - because the same fixture will scorch your plants or starve them depending purely on how high it hangs. Hang height is the cheapest, fastest lever you have over yield, and most growers get it wrong in one of two predictable ways. Here's how high to hang your light, how to match it to your tent, and the bit of kit that makes getting it right effortless.
The quick answer
- Start at 30 - 45cm above the canopy in flower for most LEDs b then fine-tune
- Too close = bleached white tips on the top leaves and a hot centre, dark edges
- Too far = even but weak light, stretchy plants and airy buds
- Match the light to the tent - a small fixture physically cannot cover a big footprint
- Hang it on ratchet hangers so you can raise it in seconds as the plant grows
How far should a grow light be from the plants?
For most LED fixtures, 30 - 45cm above the canopy in flower is the sensible starting band - 80 x 80cm tent running a ~200W board, or a 120C120cm running a 300 - 320W board, both land in that range. But treat it as a starting point, not a law. The honest answer is that the right height is wherever your light delivers the right intensity at canopy level: close enough to drive flowering, not so close it burns. A phone PAR app (or a proper meter if you want precision) lets you read the actual light hitting your canopy - take a reading in the centre and at each corner, then adjust the height to even it out.
Our Lumatek LED range lists the recommended mounting height and coverage area for each fixture, so you're not guessing from day one. Browse all grow lights here.
Why does hanging height matter so much?
Because of the inverse square law, and it's more brutal than people expect. Double the distance between light and canopy and the intensity drops to a quarter, not half. At 60cm your plants get roughly 25% of the light they'd get at 30cm; at 90cm, about 11%. That's why a light rated at "800 at 30cm" can quietly deliver veg-level intensity if you hang it at the top of the tent for "maximum coverage." The number on the box is true, at 30cm. Every centimetre you raise the light costs you real intensity, so the height you choose is doing more for your yield than almost anything else you'll fuss over.
How do I read bleaching and weak corners?
Two faults tell you the height or the light is wrong. Bleaching - pale, white-tipped leaves curling away from the light at the very top of the plant - means the intensity up there is more than the leaves can use. Raise the light 10 - 15cm and check the next day; healthy new growth confirms the fix. Weak corners - outer plants coming out smaller and stretchier than the centre, mean the light simply doesn't cover the footprint. A 100W LED in a 120 x 120cm tent will never reach the corners, full stop, because the edges always get a fraction of what the centre does.
If your corners are starved, the fix is a light sized to the space rather than to your budget. Sizing up is cheaper than a wasted grow b our grow lights are sorted by coverage area so you can match the fixture to your tent footprint at a glance.
The kit that makes height adjustment easy
Your plant grows; your light has to keep moving up to stay at the right distance. Trying to do that on a fixed chain or a knot of string is a nuisance, and most growers just stop bothering, which is how lights end up at the wrong height for half the grow. A pair of rope-ratchet hangers lets you raise or lower the fixture in seconds with one hand, and they lock solidly in place. They're a few euro and they're the single best small upgrade you can make to a tent.
Pop in and we'll match a light to your tent
If you tell us your tent size and what you're growing, we'll point you at the Lumatek that covers the footprint properly - no over-buying, no starved corners. DIG is Ireland's largest grow shop, based in Dublin, with collection available in store and delivery across Ireland.
Want the full physics behind hang height - the inverse square law explained step by step, and how to dial in PPFD at the canopy - the team at Grow Good Bud have the free in-depth guide.
FAQ
How far should my grow light be from the plants?
Most LEDs start around 30 - 45cm above the canopy in flower, but it depends on the fixture's power. Measure intensity at the canopy with a PAR app if you can, and watch for bleaching (too close) or stretching (too far).
Why are my top leaves turning white?
That's bleaching - the light is too close, and the intensity at those top leaves is more than they can use. Raise the fixture 10 x 15cm and recheck in a day; new growth should come in normal.
Why do the corners of my tent grow worse than the centre?
The light isn't covering the footprint. Intensity falls off sharply toward the edges, so an undersized fixture leaves the corners starved. Move up to a light rated for your tent size, or use a smaller tent.
Do I really need ratchet hangers?
They're not essential, but they're one of the cheapest upgrades that genuinely improves a grow. They let you raise the light as the plant grows so it stays at the right distance throughout - easy with one hand, and they lock firmly.
Where can I buy grow lights and hangers in Ireland?
DIG (Dublin Indoor Gardening) stocks Lumatek LED lights and rope-ratchet hangers, with collection in Dublin and delivery across Ireland. Tell us your tent size and we'll size the light to your footprint.