Hydroponics Q&A: Why Are Grow Lights Red And Blue?

Thomas Angas by Thomas Angas | Last Updated: April 14, 2020

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For your plants to grow well they need light. As hydroponics is predominantly done indoors this means that we need to provide our plants with artificial light and this is where a full spectrum grow light comes in. If you’re new to grow lights you might wonder why are grow lights red and blue and how do they differ from normal house bulbs?

In this post, we find out.

Why Are Grow Lights Red And Blue?

A good full spectrum grow light contains both red and blue light to provide your plants with everything they need for different stages of your plant’s development.

What Is A Grow Light?

A good full spectrum grow light has 3 distinct characteristics – it’s bright, has a good nanometer range (that is the amount of visible and invisible light) and has a good mix of red and blue light.

Can’t I Just Use Red Or Blue?

Rather than thinking of light as channels with red and blue being separate a better way to think of it is as a scale with red at one end and blue at the other. The sun naturally produces both light waves with red and light waves with blue in it and in nature your plants use both of these different types of light for different stages of their development.

As we mentioned in our guide to the best LED grow lights for seed starting, blue light is particularly useful when seeds are in the growth stage while the red light is useful for flowering and fruiting.

The problem with only using just red light or just blue light is that if for example, you were to use a red light bulb with your plant – it would become very leggy and if it has too much blue light then it’ll struggle to flower or bear fruit.

This is why we use a full spectrum light. Not only does it mean that we don’t have to mess about swapping bulbs to match the different stages of the plant’s development but it also means we can be sure that our plant is getting the exact lighting requirements that it needs.

The Bottom Line

Now you hopefully we’ve answered the question “why are grow lights red and blue?” know a little bit more about why we as indoor gardeners love to use full spectrum grow lights within our hydroponics systems and some of the benefits of using them within your system.

Happy Gardening!

Thomas Angas, the founder of Authority Gardening lives with his wife and two darling pups. He spends his free time writing, hiking and learning how to become a better gardener. He launched Authority Gardening in 2017 to help people all over the world their gardens grow.