Grow Lights for Houseplants: How to Choose and Use One
Grow lights for houseplants explained: PPFD, DLI and lux in plain English, how far away and how many hours, the best types for winter, and mistakes.
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Grow lights for houseplants are worth it when your plants don't get enough daylight: in rooms with no windows, dim north-facing flats, basements, and through dark winters. For most foliage plants, a full-spectrum white LED grow light, placed about 20–40 cm above the leaves and run for 10–14 hours a day on a timer, is enough to turn slow survival into real growth. You don't need a horticultural rig. You do need to get distance and hours right.
When do you need a grow light?
| Situation | Grow light? |
|---|---|
| Plant within a metre or two of a bright window | Usually not |
| North-facing room, plant away from the window | Often helpful |
| Room or office with no windows | Yes, essential for steady growth |
| Basement with small window wells | Yes |
| Winter in high latitudes (UK, Canada, northern US) | Helpful for light-hungry plants |
| Growing succulents, cacti or herbs indoors | Usually yes, unless on a sunny sill |
| Seedlings and cuttings | Very helpful |
A quick check: measure the spot with a free phone light meter app at midday, and convert it with our plant light meter converter. Under about 250 foot-candles (roughly 2,700 lux) is "Low light". Under 50 foot-candles (about 540 lux) is too dark for most plants without help.
Grow light terms in plain English
| Term | What it means | Why you care |
|---|---|---|
| Lux / foot-candles | Brightness as the human eye sees it | Easy to measure with a phone. Rough guide for plants. |
| PAR | The light wavelengths plants use (400–700 nm) | Grow lights are designed around it |
| PPFD (µmol/m²/s) | How much plant-usable light hits a spot each second | The best number to compare lights at a given distance |
| DLI (mol/m²/day) | Total plant-usable light in a day: PPFD × hours | What actually drives growth |
| Kelvin (K) | Colour of white light: ~2,700 K warm, ~6,500 K cool | Mostly a look preference for foliage plants |
| Watts | Power used | Not a measure of how much light reaches the plant |
Daily light integral (DLI)
DLI is the most useful idea. A plant cares about the total light it gets over a day, not just the brightness at one moment. A dimmer light on for longer can deliver the same DLI as a brighter one for fewer hours.
Our converter calculates DLI as PPFD × hours × 0.0036:
| PPFD at the leaves | Hours on | DLI (mol/m²/day) |
|---|---|---|
| 50 | 12 | 2.2 |
| 100 | 12 | 4.3 |
| 150 | 12 | 6.5 |
| 200 | 12 | 8.6 |
| 200 | 14 | 10.1 |
| 300 | 12 | 13 |
As a rough guide, low-light foliage plants such as ZZ plants, pothos and snake plants manage in the low single digits. Most foliage plants grow well somewhere in the mid single digits to around 10. High-light plants like succulents, cacti and herbs want more. Treat these as ballpark ranges and watch the plant.
Types of grow lights for houseplants
| Type | Good for | Pros | Cons |
|---|---|---|---|
| LED grow bulb (E27/E26 screw-in) | 1–3 plants in an existing lamp | Cheap, simple | Small coverage, can be dim at a distance |
| Clip-on LED with flexible arms | Desk plants, single shelves | Easy to aim, often has timer | Small coverage |
| LED strip or bar | Shelves and plant cabinets | Even light along a shelf | Needs mounting |
| LED panel | Plant stands, many plants | Strong, even coverage | More expensive, can be bright to look at |
| Fluorescent tube (T5) | Shelves, seedlings | Even, proven | Being phased out, less efficient than LED |
For most homes, full-spectrum white LEDs are the right choice. Purple or "blurple" lights work for plants but make leaves look odd and are tiring to live with.
How to set up a grow light
- Pick the right size. A clip-on lamp for one plant, a bar or panel for a shelf.
- Set the distance. Start around 20–40 cm above the leaves for small LEDs. If the maker gives a PPFD chart, use it to hit roughly 100–200 µmol/m²/s at the leaves for foliage plants.
- Set a timer. 10–14 hours a day. Consistency matters more than perfection.
- Watch the plant for two weeks. Leggy growth and leaning means not enough light. Bleaching, crisping or curled leaves near the lamp means too much or too close.
- Adjust one thing at a time. Change height or hours, not both together.
Worked example
A small LED bar sits 30 cm above a shelf of pothos and a peace lily. The maker's chart says about 150 µmol/m²/s at that distance. On a 12-hour timer, the DLI is 150 × 12 × 0.0036 ≈ 6.5 mol/m²/day. That's plenty for those plants. For a succulent on the same shelf, you'd move it to the centre of the bar, closer to the light, or give it its own brighter lamp.
Grow lights in winter
Short, grey days in northern winters can drop indoor light a long way. Plants that grew happily by a window in summer may stretch, stop growing or drop leaves. A grow light run for 10–12 hours in the darker months tops them up. You'll also see slightly faster soil drying, so check soil more often. Our watering schedule builder uses longer check intervals for the dormant season, but if you're adding a strong grow light, the plant may behave more like it does in summer.
Grow lights for specific situations
- Windowless office or room: a small LED on a timer covering working hours plus a little extra. See plants for an office with no windows.
- Bathroom with no window: choose a light rated for damp locations and keep it away from water. See bathroom plants.
- Dark corner: a floor-standing lamp with a grow bulb turns a "survive" spot into a "grow" spot. See very low light plants.
- Monstera without split leaves: a strong grow light is one of the fastest ways to fix it. See our monstera deliciosa care guide.
Common grow light mistakes
- Light too far away. Light intensity falls off quickly with distance. A lamp a metre above a plant may deliver a fraction of what the box suggests.
- Judging by watts. Two lights with the same wattage can produce very different amounts of usable light.
- Leaving it on 24/7. Plants need darkness. 10–14 hours is enough.
- No timer. Forgetting to switch it on or off makes the DLI unpredictable.
- Too close too soon. Moving a plant from a dim room to directly under a strong light can bleach leaves. Increase gradually.
- Not watering more. Faster growth uses more water. Check soil more often after adding a light.
What to look for when buying
- A PPFD chart or figure at a stated distance. It's the most useful spec. Lights that only list watts or "equivalent" watts are harder to compare.
- Full-spectrum white light, roughly 3,000–6,500 K, so plants look natural.
- A built-in or plug-in timer.
- Adjustable height or arms, so you can change the distance as plants grow.
- Coverage that matches your shelf. A bar the length of the shelf beats a single bulb in the middle.
- Low heat at the leaves. LEDs run cool, but check the housing doesn't get hot near leaves.
Safety
- Use lights designed for indoor home use, with proper certification for your country.
- Keep cables and plugs away from water and saucers.
- Don't stare into strong LEDs, and angle panels away from eyes.
- Make sure fittings are rated for the bulb wattage and, in bathrooms, for damp locations.
Sources and further reading
- Royal Horticultural Society, on lighting for houseplants and seedlings.
- Penn State Extension, on supplemental lighting, PPFD and daily light integral.
- Utah State University Extension, on the basics of LED grow lights.
To check what your space gets before buying, start with the plant light meter converter, and compare plants by light level with the low-light plant finder.
Frequently asked questions
Do houseplants need grow lights?
Not if they get enough daylight. A grow light helps in dark rooms, windowless spaces, basements, north-facing flats and during short winter days, or when you want plants that need more light than your windows give.
How many hours a day should a grow light be on for houseplants?
Around 10 to 14 hours for most foliage houseplants. Use a timer so it's consistent. Plants also need a dark period, so don't leave the light on 24 hours a day.
How far should a grow light be from plants?
It depends on the light's strength. Many small LED grow lights work well 20 to 40 cm above the leaves. Stronger panels may need to be higher. Check the maker's PPFD chart if there is one, and move the light up if leaves bleach or crisp.
Can I use a regular LED bulb as a grow light?
Yes, plants can grow under ordinary white LED bulbs. They just tend to be less bright at plant level than a grow light of the same wattage design. Put the bulb close to the plants and run it for longer hours.
Are purple grow lights better than white?
Not for houseplants in a living space. Plants use red and blue light efficiently, but full-spectrum white LEDs grow foliage plants well, show the plant's true colours and are far nicer to live with.