Frequently asked questions about growing
What distance should my light be above my plant?
The distance from the light to the plant canopy is a large factor in determining the intensity of light (umol/s) falling on the plant. This means it can be used to approximate the amount of light a plant is receiving but only if we know the other factors such as the light's power consumption (in Watts) and its efficiency (umol/J). While this approximation is possible it is more accurate to simply measure the light at the canopy using a smartphone or lux meter and do away with the distance meaurement.
The light intensity of the relevant frequency for photosynthesis is called PPFD and its unit of intensity is umol/s (Micromols per second). Measuring light intensity (rather than calculating it) makes it much easier to perfect light conditions even in cases where the grow light's efficiency or consumption is unknown.
This question is very common because light manufacturers often suggest distances to use.