Grow lights for plants: when do you need one and which should you choose?

It is September, and your plants can tell. The days are getting shorter, the sun sits lower and the light coming through the window is far weaker than it was in June. Plants that did fine all summer suddenly droop, put out long thin stems or simply stop growing. In most cases there is nothing wrong with your watering or your feeding: there is not enough light. A grow light fixes that.

Why your plants are short on light right now

A good deal of the outdoor light is already lost through glass, and in winter that outdoor light is itself a fraction of what it was in summer. A spot that feels bright in July is dark to a plant in November. A few signs give it away: stems stretching towards the window, pale or small new leaves, wide gaps between the leaves, and buds that never open. A grow lamp gives the plant the light it no longer gets from the window during these months.

Red, blue or full spectrum?

Plants mainly use red and blue light for photosynthesis. Blue light produces compact, sturdy growth and good foliage. Red light pushes the plant towards flowering and fruit set. Lamps that emit only those two colours are easy to spot by their purple glow. They are efficient, because no energy goes into colours the plant barely uses.

Full spectrum lamps give white light and do essentially the same job, but they are far more pleasant to sit next to. For a greenhouse or a corner you do not spend time in, red and blue is the logical choice. If the lamp is in your living room, you probably want white light.

Which grow light suits your situation?

For one or two plants in a dark spot, a single bulb with an E27 fitting is the simplest option: it screws into any existing socket. Our E27 grow light bulb with red and blue light comes with either 80 or 300 LEDs.

If you want to light several plants at once, a panel becomes interesting. The 40 watt LED grow light panel covers a decent area with its 164 LEDs, stays cool thanks to the aluminium housing and makes no noise at all, because there is no fan inside.

If your plants are spread out, an E27 splitter lets you run three or five lamps from a single socket.

👉 Browse all grow lights and plant lamps

Hanging height and running hours

Hang the lamp 20 to 40 cm above the plant. Too close and you scorch the leaves; too far and the effect drops away quickly, because light intensity falls off sharply with distance. As a rule of thumb for running hours: seedlings and cuttings 16 to 18 hours a day, young plants 14 to 16 hours, and mature plants 12 to 14 hours. If the plant gets no daylight at all, the lamp can stay on longer. Do not run it around the clock though: plenty happens inside a plant during the dark hours too.

Measure instead of guessing

Whether a spot is genuinely too dark is hard to judge by eye. Our eyes adapt, so 500 lux already reads as bright to us while many plants will not grow in it. With a light meter you can see at a glance how much light actually reaches that spot, and whether your lamp is hanging at the right height. That saves you a season of trial and error.

In short

Less light indoors does not mean your plants have to struggle for half the year. Pick a lamp that matches the number of plants and the room, hang it at the right height and keep the running hours consistent. Do that, and your plants will keep growing in January just as well as they did in June.