Grow Light CheckPlacement guide
How far should a grow light be from a plant?
There is no dependable distance based on wattage alone. Begin with measured or published light output, account for the beam and fixture shape, and adjust at the height of the leaves.
Published and reviewed by Grow Light Check ยท Updated
A practical distance process
- Identify PPFD at a known distance, PPF, PPE plus actual watts, CBCP, or lumens for an ordinary white LED.
- Choose the plant and the approximate illuminated area.
- Calculate intensity at several distances and compare PPFD and DLI with the plant target.
- Start conservatively, then check new growth, leaf temperature and color.
Why two lights with the same watts need different distances
A narrow reflector sends more of its output into a small area. A diffuse bulb or long bar spreads output more widely. A 20-watt narrow-beam lamp can therefore be much brighter at one leaf than a higher-wattage fixture designed to cover a shelf.
Distance also changes coverage: moving a light closer usually increases the center intensity while shrinking the evenly lit area.
Use the result as a starting point
A listed wattage is electricity use, not plant-level brightness. Reflectors, lenses, fixture dimensions, spectrum, barriers, and the illuminated area all affect the result. Manufacturer PPFD maps or a reading from a cosine-corrected quantum meter are stronger evidence than wattage alone.