Tell it where the window is and which way it faces. It estimates the light a plant would get at that spot in every month of the year, then lists the plants that will grow there.

What the numbers mean

The planner works in daily light integral (DLI): the total amount of photosynthetic light that lands on a square meter in a day, in moles of photons. It is the number growers use because it adds up brightness and day length together. Bright summer sun outdoors gives 40 to 60; a spot a few feet back from a north window in winter can get less than 1.

Plants are matched with thresholds from extension services: roughly 3 for low-light plants to keep growing, 6 for medium light, 10 for bright indirect light and 12 or more for sun-loving plants such as succulents and herbs. Below those levels a plant can hold on for a while, but it stops growing. The light units converter turns a light-meter reading in lux or foot-candles into the same units.

This is an estimate from sun geometry and typical weather, not a measurement. Curtains, dirty glass, a wall painted dark, a tree that leafs out in May: all of these change the real number. If you own a light meter, measure your spot and compare. Read exactly how it is calculated, with sources.

Month	Dull	Typical	Bright	Direct sun on the spot	Day length
Jan	1.4	1.4	1.5	0.0 h	9.4 h
Feb	2.3	2.4	2.6	0.4 h	10.5 h
Mar	3.6	4.5	5.6	1.8 h	11.7 h
Apr	4.9	6.5	8.5	3.2 h	13.1 h
May	5.7	7.6	10	4.1 h	14.3 h
Jun	6.0	7.9	10	4.3 h	14.9 h
Jul	5.8	7.7	10	4.2 h	14.6 h
Aug	5.3	7.0	9.3	3.7 h	13.6 h
Sep	4.1	5.3	6.8	2.3 h	12.2 h
Oct	2.7	3.1	3.7	0.9 h	10.9 h
Nov	1.5	1.6	1.6	0.0 h	9.7 h
Dec	1.2	1.3	1.4	0.0 h	9.1 h

Window Light Planner

You can grow these 50 plants

Grows well, but dim in the darkest months 1

Survives here, slow growth 49

What the numbers mean

Window Light Planner

Results

You can grow these 50 plants

Grows well, but dim in the darkest months 1

Survives here, slow growth 49

What the numbers mean