Measuring Light Before Buying Plants

"Bright indirect light" is the least useful phrase in horticulture. It describes a range of roughly 800 to 20,000 lux, which is the difference between a plant that grows and a plant that slowly dismantles itself. A free lux meter app, held flat against the wall where the pot will actually sit, resolves it in one afternoon.

Take four readings

On the sill, midday — the ceiling of what that window can offer.
One metre back — usually a 70–80% drop, which is the number that surprises people.
Same spots at 16:00 — winter afternoon light is the real constraint, not summer noon.
With the blind as you normally leave it — measuring the room you live in, not an idealised one.

Two metres from a north window the meter reads under 400 lux, which rules out most of what is sold as easy.

What survives at each level

Measured lux	Realistic choices
Under 500	Aspidistra, ZZ plant, snake plant — slow but stable
500–1,500	Pothos, philodendron, ferns with humidity
1,500–5,000	Most calathea, begonia, peperomia
Over 10,000	Succulents, citrus, herbs that actually crop

Everything in the first row will also live in the third. Nothing in the last row will live in the first, regardless of care, feeding or advice from the shop.

You cannot water a plant into having more light. Almost every houseplant death we have investigated started as a light problem and was finished by the watering can.

Then fix watering to the light

Low light means slow transpiration, which means a pot stays wet for a fortnight and roots rot. Weigh the pot after a full water and again when the top five centimetres are dry — the difference is your watering interval in grams, which is far more reliable than a schedule. In a dim room that interval is often three weeks in winter.