☀️ Light Level Reference Chart

A quick reference for translating light meter readings (foot-candles or lux) into the descriptive light categories used on plant care guides. Actual plant needs still vary by species — use this as a general starting point.

How the two scales line up

Foot-candles and lux measure the same thing in different units, one lumen per square foot against one lumen per square metre:

lux = foot-candles × 10.764        foot-candles = lux / 10.764

That is where the chart's bands come from: 250 fc is 2,691 lux, rounded to 2,700, and the 2,500 fc line lands on 26,910, shown as 27,000. The category names themselves are the interiorscape convention that plant labels and extension horticulture guides use; they are descriptive bands, not a standard anyone certifies.

Taking a reading that means something

Measure at the plant, not the window. Hold the meter where the leaves are, sensor pointing at the light source. Light falls off sharply with distance — a spot three feet back from the glass can read a quarter of one sitting on the sill.
Read at several times of day. An east window is bright at 09:00 and dim by 15:00. The number that matters is the typical level across the hours the plant is lit, not the single best moment.
Phone light-meter apps read lux from the front camera sensor and are rough, often 20% or more out, but they are consistent enough to compare one spot in your home with another.

Indoor light is dimmer than it feels. Open shade outdoors runs around 1,000 fc and full summer sun about 10,000 fc, so even the “direct sun” band here is a fraction of what a plant would get on a patio.

Frequently asked questions

How many lux is bright indirect light?

Roughly 10,800 to 27,000 lux, which is 1,000 to 2,500 foot-candles. In practice that is a position near a bright window where the sun itself is filtered by sheer curtain or is off to one side.

What is 1 foot-candle in lux?

10.764 lux, because a square metre is 10.764 square feet. To go the other way, divide your lux reading by the same number.

Is a north-facing window low light or medium light?

Usually medium, around 250 to 1,000 fc within a couple of feet of the glass in the northern hemisphere, dropping to low light further into the room. South of the equator the same applies to a south window.