Grow Light Distance and Stretching
Light distance is the simplest lever you have and one of the easiest to get wrong. Move a light too far and plants reach for it desperately, growing tall and weak. Move it too close and leaves curl, bleach, or develop scorched edges that never recover. The right distance isn't a printed number on the box — it is a moving target that changes with your plant's stage and your fixture's actual output.
The inverse-square law in practice
Double the distance from the light source and the intensity drops to roughly one-quarter, not one-half. This means the difference between fifteen and thirty centimetres is far larger than the difference between forty-five and sixty — small moves close to the fixture matter a lot. The law applies perfectly to a point source in open air, and in a reflective tent with multiple fixtures the falloff is gentler, but the principle holds: light gets weaker fast as you pull away, and you cannot compensate by simply running the light longer.
Too far — etiolation and what it looks like
When a plant decides it isn't getting enough light, its growth strategy shifts: it stretches toward whatever light it can find, producing abnormally long stems between each node. The stems are thin, the leaves are spaced far apart and stay small, and the whole plant takes on a pale, lanky appearance. This is not a cosmetic issue — those stretched stems will never thicken to support heavy flowers or fruit later, and the light that eventually reaches the lower canopy after stretch has already been wasted on stem length rather than leaf area.
Too close — light burn and heat stress
The first sign of a light that is too close is usually the uppermost leaves: they curl upward at the edges, sometimes described as canoeing or tacoing, as the leaf tries to reduce surface area exposed to the light. If the fixture runs hot, you may also see the leaf edges dry out and turn crispy while the rest of the plant looks healthy, because radiant heat damage is localised to the top of the canopy. A bleached-white appearance on the highest buds or newest growth is a later, more serious stage of light stress — that chlorophyll is gone and won't come back in those tissues.
Finding the sweet spot
The manufacturer's recommended hanging height is a starting point, not a rule. Use a PPFD measurement at canopy level to validate it, then watch the plant's response over the next three to five days. New growth staying compact with healthy green colour means you are in range. If internodes start stretching, lower the light in small increments — five centimetres at a time — and check again. If the top leaves show any curling or pale tips, raise it back up. The goal is the closest distance that the plant accepts without showing stress signals.
Key takeaway
Move the light as close as the plant tolerates without stress signs, measured by PPFD at canopy height, not by a fixed hanging chart.