For a long time, we gave plants light in the greenhouses that were made for the human eyes, namely yellow greenish light and blue greenish light. This because the installed lights in the greenhouses were also the lights we used in our homes, and our human eyes see things the best under these colours. For optimal plant growth, plants require lights with specific wavelengths that can be well absorbed by the plant pigments to drive photosysnthesis.

The most abundant light absorbing pigments for photosynthesis in plants (chlorophyll) are sensitive to red and blue light (= they absorb red and blue light the best). This insight and the development of more efficient and cheaper LED lights, led to the implementation of more red and blue LED grow lamps in greenhouses and indoor farming environments such as vertical farms.

Pink lights in greenhouses

When red and blue light are given together, we see this light as pink. To answer the question why do greenhouses use pink lights, it is because this colour combination drives photosynthesis the effectively and efficiently. Some people consider this light combination also as purple.