Guide · Question & answer

Grow light instead of sun: is a grow light worth it?

Yes, when no direct sunlight reaches the plant: a good full-spectrum grow light helps houseplants through a dark room or a grey winter. It stands in for the sun only at close range and only while it is switched on, and direct sunlight is many times brighter. If there is a spot outside that gets sun, a heliostat can redirect real sunlight through the window to the plant, and the lamp covers the rest.

When a grow light makes sense

• No sun at the plant: deep inside a north-facing room, in a corner, or in a room whose window looks onto a wall.
• Winter: short, grey days, when even a bright window gives a plant too little light.
• Seedlings in spring: young plants grow long and thin when the light is too weak.
• Sun-hungry plants in a shaded room: a lemon tree, cacti or a large monstera want more light than most living rooms offer.

If the plant already stands in a window that gets a few hours of direct sun, a lamp adds little. Then a better spot by the window does more.

What the sun does that a lamp doesn't

Brightness. Direct sunlight is many times brighter than a grow light at a normal distance. The lamp makes up for it with closeness and long hours.

Area. A lamp mostly lights the area right below it. The further away the plant stands, the less light reaches its leaves, and that drops off quickly.

Spectrum. Full-spectrum LEDs come close to daylight. Sunlight is the original, with all the colours plants have adapted to.

Running. A lamp needs a socket, a timer and electricity every day. The sun costs nothing, but it only shines when the weather allows.

Grow light, ordinary LED or daylight lamp?

• Ordinary LED bulb: bright enough for your eyes, usually far too weak for plants once it hangs from the ceiling.
• Daylight lamp: made for people sitting in front of it, not for lighting leaves from above for hours. For plants it is usually the wrong tool.
• Full-spectrum grow light: white light, built for plants. In a living room it is more pleasant than the purple light of red-blue lamps.

Whichever lamp you choose: put it on a timer so it runs the same length every day, and follow the manufacturer's advice on distance and hours for your plant.

The third option: bring real sun to the plant

Many dark rooms are dark only because the sun doesn't reach them, while it shines on the courtyard, the terrace or the garden. A heliostat stands in that sunny spot, follows the sun and redirects its light through the window onto the plant. It delivers real sunlight for the hours the sun reaches the mirror. Not around the clock, which is why it pairs well with a grow light: sun whenever there is sun, the lamp in the evening and on grey days. How a plant responds depends on its species, the sun hours at your location, the room and your care.

Grow light or heliostat

Frequently asked questions

Is a grow light worth it?

Yes, if no direct sunlight reaches the plant, for example deep inside a north-facing room or in winter. If the plant already gets a few hours of direct sun at the window, a lamp adds little.

Can a grow light replace sunlight?

Partly. A good full-spectrum lamp helps many houseplants through the winter, but only at close range and only while it is on. Direct sunlight is many times brighter and lights a larger area.

Grow light or daylight lamp: which is better for plants?

A grow light. A daylight lamp is made for people; a grow light is made to light leaves from close by for many hours.

Can plants grow without sunlight?

With enough artificial light, yes. Without any light, no. Shade plants get by with little light, but not with none.

How do I get real sun to a plant in a dark room?

With a heliostat: a mirror outside in a sunny spot follows the sun and redirects its light through the window onto the plant. It needs a spot outside that gets sun and can see the window.