Houseplant Light Requirement Calculator

Work out houseplant light requirement instantly with clear inputs, formula shown and shareable results.

About Houseplant Light Requirement Calculator

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.

Formulas

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

Worked example

With the default values below, Houseplant Light Requirement Calculator returns Estimated light level at the plant of 2,000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Distance from the windowminimum 0.1 m: 2 m
Window orientationone of South facing (up to 10,000 lux at the glass), East or west facing (5,000 lux), North facing (2,000 lux): South facing (up to 10,000 lux at the glass)
Light lost to blinds or obstructionaccepts 0–95 %: 20 %

Results

Estimated light level at the plant: 2,000 lux
Light category: Medium light - suits pothos and philodendron
Light level at the glass after obstruction: 8,000 lux
Approximate daily light integral: 1.598 mol/m2/day

Step by step

1Values used
2Light at the plant
3Daily light integral
4Estimated light level at the plant= 2,000 lux
5Light category= Medium light - suits pothos and philodendron
6Light level at the glass after obstruction= 8,000 lux
7Approximate daily light integral= 1.598 mol/m2/day

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Houseplant Light Requirement figure worked out?

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.

Why does this matter?

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.

What do I need to enter?

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.