Does Your Plant Have Enough Light? The Two-Minute Light Test
Short answer: most houseplants that stall indoors are short of light, not water. "Bright indirect light" on the care tag is not a number, so here is a two-minute test that gives you one, and the two numbers that actually matter.
The two-minute light test
Answer each one honestly and keep a rough tally.
1. Where does your plant sit?
- Within 1 metre of a bright window, blinds open most of the day — 0 points
- Near a window, but tinted glass, sheer curtains, or blinds usually closed — 1 point
- More than 1 metre from any window, or in a corner or hallway — 2 points
2. Does that window ever get direct sun?
- Yes, sun lands on the sill for part of most days — 0 points
- Bright, but the sun never quite reaches in — 1 point
- Soft light all day, never direct — 2 points
3. What kind of plant is it?
- Pothos, ZZ, Sansevieria, Peace Lily, most Begonias including rex — 0 points
- Philodendron (green forms), Hoyas — 1 point
- Monstera, Alocasia, Caladium, Anthurium, anything with heavy variegation — 2 points
4. What does the plant actually look like?
- Compact, colourful, new leaves the same size as the old ones — 0 points
- Slightly leggy, leaves reaching for the window, new growth smaller — 1 point
- Long gaps between leaves, pale new growth, variegation reverting to green — 2 points
5. After sunset, could you read a book comfortably in that room?
- Anywhere in the room — 0 points
- Only near a lamp — 1 point
- Warm, dim, mood-lighting kind of room — 2 points
What your score means
0–2: you don't need more light
Adding a grow light won't hurt, but it isn't what's holding your plant back. Look at watering, humidity or roots instead.
3–5: more light would help, but it isn't urgent
You'll see fuller growth, better colour and less stretching. The plant will live without it.
6–8: your plant needs more light
It is stretching for light it can't reach, and it will keep declining. This is the one change that moves the needle.
9–10: it needed light three months ago
Real light stress. A grow light plus a bit of patience brings it back. Without one, it's a slow decline.
The two numbers that matter
Skip the phrase on the tag. Measure the spot with a free lux-meter app on your phone. Hold the phone where the leaf sits, screen facing the light, and read it. Then compare:
| Reading at the leaf | What it means |
|---|---|
| Under about 1,000 lux (about 15 µmol/s/m²) | Surviving, not growing. Leaves eventually drop. |
| Around 4,000 lux (about 60 µmol/s/m²), 12 hours a day | Growing properly. New leaves as big as the old ones. |
| Heavily variegated plant | Double it. The white parts of the leaf make no food. |
Light drops off faster than your eyes tell you. One measured room read about 4,300 lux at the glass and under 1,000 a few feet back. The room still looked bright. Your eyes adjust. The plant can't.
Lux is not what the plant sees. Lux is brightness weighted to the human eye. Plants use the whole 400–700 nm band, measured as PPFD in µmol/s/m². The conversion depends on the light source: in sunlight 1 µmol/s/m² is about 54 lux, under a white LED about 67–70. That is why a phone app is a screening tool, not a spec, and why the table above gives both.
If the spot doesn't have it
Stop moving the plant from window to window. Add light. Any full-spectrum grow bulb in a normal lamp, 30–50 cm above the leaves, on a timer for 12 hours, takes a "surviving" spot to a "growing" one. Closer than 30 cm and sensitive leaves burn; further than 50 cm and the intensity drops off fast.
We don't have a single sunny window in the shop. Everything here grows under a bulb in a normal lamp.
Get the light test by email, plus the follow-ups
The two numbers, how to read your phone meter properly, and what to do when the reading is low. Occasional emails, unsubscribe any time.
In the UAE? These are the bulbs I stock
Three SANSI options, all full-spectrum, all ship across the UAE. The 36W is the safe bet for most rooms. The clip-on has its own timer.
- SANSI 36W bulb (E27) — one demanding plant or a deep shelf
- SANSI 24W bulb (E27) — one low or medium-light plant
- SANSI dual-head clip-on with timer — two plants, no lamp needed
The full Dubai guide, with the five factors for choosing between them, is here: Do you need a grow light in Dubai?
Frequently asked questions
What does "bright indirect light" actually mean?
Nothing precise. Four popular guides define it anywhere from about 1,000 to 20,000 lux, a twenty-fold range under the same three words. Measure your spot instead.
Is a phone lux-meter app accurate enough?
It is a screening tool. Phone sensors vary and lux is eye-weighted, not plant-weighted. It is still far better than a phrase on a tag, and it tells you reliably whether a spot is under 1,000 or around 4,000.
What is PPFD?
Photosynthetic Photon Flux Density: how many usable photons, in the 400–700 nm band, land on a square metre each second, in µmol/s/m². It is the number on a grow-light spec sheet. Divide lux by about 54 for sunlight or about 67–70 for a white LED to estimate it.
How far from the window is too far?
There is no fixed distance. Light falls off quickly and depends on the glass, the curtains and what is outside. In one measured room the reading dropped from about 4,300 lux at the glass to under 1,000 a few feet back. Measure the spot, not the window.
Do I need a grow light?
Take the test above. A score of 6 or more, or a reading under about 1,000 lux where the plant sits, means yes.
Written by Faseela
I run Faseela Flowers and Plants, an online plant shop in the UAE. Rare aroids, quality substrates and the grow lights I use on my own shelves.