Work out houseplant light requirement instantly with clear inputs, formula shown and shareable results.
Light falls with the inverse square of distance from the window, so the level at the plant is the level at the glass divided by the distance in metres squared, after obstruction losses. The inverse square law is brutal indoors: moving a plant from one metre to three cuts its light to a ninth, which explains most unexplained houseplant decline.
Light at the plant
lux = lux at the glass x (1 - obstruction) / distance in metres squared
Daily light integral
DLI = lux x 0.0185 x seconds of light per day / 1,000,000
lux = lux at the glass x (1 - obstruction) / distance in metres squared. Light falls with the inverse square of distance from the window, so the level at the plant is the level at the glass divided by the distance in metres squared, after obstruction losses.
The inverse square law is brutal indoors: moving a plant from one metre to three cuts its light to a ninth, which explains most unexplained houseplant decline.
Enter distance from the window, window orientation, light lost to blinds or obstruction. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.