When and how to use growing lights

When and how to use growing lights

In this article we will talk about using artificial light when growing plants. Is it really needed, and what light should you use? What about these pink "grow lights" that have become common the last years?

Why is light needed when growing?

Plants have evolved to grow using natural sunlight. When growing inside, putting your plant by a window is enough, unless you grow during the winter in the northern or southern parts of the world. But how much daylight is enough daylight? In our experience, if you have less than 10 hours of daylight, some kind of artificial light is needed. The needs differ from plant to plant - some need less and some need more. This ”rule” also assumes you actually want your plant to grow and get bigger - if you only want your plant to survive, you can do without a lamp. In this article, though, we are concerned with growing herbs, vegetables and salad greens from a seed, which requires energy! And neither UV lights or heat lamps will do - only visible light.

So what kind of light is needed?

You might have seen them before, those lamps that emits a kind of pink light from red and blue LEDs. They are usually called ”grow lights” and are built this way based on the realization that plants don’t use all wavelengths of light equally. Research has shown that the chlorophyll in plant cells mostly make use of red and blue wavelengths of the visible light spectrum. Leaves are green, simply because a lot of green light are reflected from them rather that being used!

It is true that they use mostly red and blue light, but it needs other parts of the spectrum too, such as green and yellow, in order to grow optimally.

We have grown chili, basil and other edibles inside for many years, and in our experience white light from fluorescent lamps, LED ar CFL’s work better than ”red and blue growing lights”.  These provide a broad spectrum of light that is not limited to particular wavelengths. Also, most people would agree that white light looks much better than red and blue ”disco”-lights!  Incandescent lamps generate more heat than light and should be avoided. When it comes to indoor growing, you want a lamp that generates a lot of white light.

botanium windowsill

Fluorescent lamps and CFL

This kind of light is reliable, cheap and easy to find. They last a long time, but not as long as LEDs. It’s easy to find rather powerful ones, and different lamps are easy to compare since they usually have similar spectrums. They come in ”warm light” and ”cold light” variants, and you can use either. It’s really not a big difference in plant growth. Keep it simple, and go for a powerful lamp. A 20 watt CFL is a good choice for a Botanium plant. If you have several plants, you can hang a T5 fluorescent lamp above them. 100 watt T5 goes a long way.


LED is the future of indoor gardening. They are smaller, last longer and are becoming more efficient that fluorescent lamps. They also more environmentally friendly, as the don’t contain any mercury. LED lamps marketed as ”growing lamps” are generally more expensive, but you don’t need these to grow plants. A 15 Watt LED lamp Is good enough for a small Botanium plant. If you’re into DIY then you can build a powerful, cheap LED lamp for a fraction of the prize. Ledgardener.com  has DIY guides for this purpose.

How long should the lights be on?

Using a simple timer you connect to the outlet, have the lamp on for at least 12 hours per day. Because light quickly becomes weaker with distance, put the light as close to the plant as possible, without actually touching it. To be exact: doubling the distance results in a only quarter of the light making it to the plant.


So in short: use LED, fluorescent lights or CFL if you have less than 10 hours of daylight per day and grow from a seed. Use white light, and put it close to the plant for 12 hours per day. :)

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