How to read houseplant light requirements

Light is the single most important variable for an indoor plant. Get it close to right and an average plant survives almost any other mistake. Get it wrong and even an attentive owner watches their plant slowly fade. The labels at garden centres — "low light", "bright indirect", "full sun" — are not interchangeable, and the difference between them is bigger than most beginners realise.

What the four common labels actually mean

The Royal Horticultural Society groups indoor light into four practical categories, measured either in lux or by where the plant sits relative to a window.

Direct sun (more than 25,000 lux)

Sunlight hits the leaves with no filter for at least four to six hours per day. South-facing windows in the northern hemisphere, or north-facing in the southern, with no curtain. Cacti, most succulents, and some citrus need this.

Bright indirect (10,000 – 20,000 lux)

The plant sits within a metre or two of a sunny window, but not in the path of the beam. Behind a sheer curtain on a south window counts. So does an east window where direct sun only hits for the first hour or two of morning. Most popular tropicals — Monstera, Fiddle Leaf Fig, Philodendron — want this.

Medium indirect (5,000 – 10,000 lux)

Two to three metres back from a bright window, or right next to a north window. Bright enough to read a book without a lamp at noon, but never enough to cast sharp shadows. Pothos and Peace Lily live here happily.

Low light (500 – 2,500 lux)

North-facing rooms, hallways, and corners more than three metres from any window. Snake Plant, ZZ, and Aloe Vera survive here, but most plants will stretch and slow. "Low light tolerant" does not mean "thrives in low light" — it means it will not die quickly.

How to test your light without a meter

You do not need to buy anything. Two free methods give you a usable answer.

The shadow test

At noon on a clear day, hold your hand a foot above where the plant will sit and look at the shadow it casts.

• Sharp, dark shadow with crisp edges: direct sun.
• Soft shadow with fuzzy edges: bright indirect.
• Faint shadow you have to look for: medium indirect.
• No visible shadow: low light. Most plants will struggle.

The phone lux meter

Most modern phones have ambient light sensors. Free apps like Lux Light Meter (iOS) or Lux Meter (Android) read out lux directly. Hold the phone where the leaves will be, screen facing the same direction the leaves face, and check the reading at noon. Cross-reference with the ranges above. Phone meters are not laboratory accurate — readings can vary 20–30% — but they are good enough to tell bright indirect from medium indirect.

Direction matters as much as distance

Two windows the same size in the same room give very different light depending on which way they face. In the northern hemisphere:

• South: the brightest light, with several hours of direct sun in winter. Best for cacti and succulents. Most tropicals need a sheer curtain or a metre of pullback.
• East: direct morning sun until about 11am, bright indirect for the rest of the day. The sweet spot for most popular tropicals.
• West: bright indirect until afternoon, then direct afternoon sun, which is more intense than morning sun. A sheer curtain helps.
• North: consistent, gentle indirect light all day, no direct sun. Perfect for low-light plants. Most tropicals will survive but grow slowly.

Reverse the directions if you live in the southern hemisphere.

How plants tell you the light is wrong

Plants are honest. They show you within a few weeks.

• Too little light: stretched stems with long gaps between leaves (etiolation), pale or yellowing new growth, smaller leaves than the older ones, vining plants that lean hard toward the window.
• Too much direct sun: bleached patches on the leaves facing the window, crispy brown edges that appear within hours of a hot afternoon, leaves that feel hot to the touch.
• Right amount of light: new leaves emerge the same size as older ones, compact growth, no leaning, healthy colour.

Quick matchmaker

If you only know the direction your window faces, start here:

• North window or no window in sight: see our low-light plant list.
• East window: see bright indirect picks. This is the friendliest light direction.
• South or west window with a curtain: bright indirect picks again. Without a curtain, you can keep cacti and succulents.

Light category ranges adapted from the Royal Horticultural Society "Houseplants: choosing the right one" advice and Missouri Botanical Garden's "Light requirements for indoor plants".