What is the difference between blue and red spectrum light for plants?

Filed Under (Plant Lighting) by Chilli Willy on 23-10-2012

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Blue and red spectrum light are the 2 main areas of the lighting spectrum that plants need to grow.

White / blue spectrum light is more suited for propagating and is more for the early stages of plant growth (vegetative phase).  Red spectrum light is required more when your plants are flowering and fruiting (blooming phase).


There are several types of grow lights available, including fluorescent grow lights, HID grow lights and LED grow lights.

If you are looking for more information on what type of grow light you need, then you may want to read the guide we put together explaining the different types of grow light.


All types of grow light have their own grow light bulbs which provide red and blue light:

Fluorescent grow lights have fluorescent tubes that can easily be swapped between propagating (white/ blue) and flowering bulbs (red).

HID grow lights have 2 different bulbs with drastically different colour ranges, making them excellent at producing vast amounts of light in the required range, as can be clearly seen when they are operating.   For example, you can use a Metal Halide (MH) bulb for the white spectrum, like used for floodlights and a High Pressure Sodium (HPS) bulb for the red spectrum, like used for street lights.

LED grow lights simply use different coloured LED chips, either in panels of the same colour, or a mixed cluster.


Whatever grow light fixture you choose, you’ll also be able to obtain dual spectrum bulbs, which do a bit of both and are good all rounders for plant growth.

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