Looking at red light - a time telling tale

Detecting the change of season is key to a plant's survival - seasonal changes control everything from germination to vegetative growth and flowering. While temperature and light intensity influence plant growth, they are not always a reliable indicator of seasons because they may change from year to year – particularly as climate change impacts weather patterns.


So how do plants detect the change of seasons?

The Dark Side of the Moon

The Dark Side of the Moon by Plink Floyd showing how light is split into separate colour spectrums. 

Put simply, plants tell time through the wavelengths of light that they are exposed to. Sunlight is made up of a variety of different wavelengths of light (think the beam of light splitting into a rainbow on Pink Floyd’s iconic Dark Side of the Moon album cover). Each wavelength has a different effect on a plant’s physiological growth. Light in the red and far-red end of the spectrum (around 620 to 780 nanometers) controls how plants tell time – a function called photoperiodism

Plants produce light-sensitive proteins called phytochromes that detect light. These phytochromes essentially act as a switch – when a plant absorbs red light (around 620 to 700 nanometers), it activates the protein that encourages it to grow. Conversely, when it absorbs far-red light (around 700 to 780 nanometers), it activates the protein that makes plants dormant.

Light sensitive proteins become active during the day when plants are exposed to red rich, far-red deficient full sun. These same proteins become dormant at night when red light slowly decays to far-red light.

 Unfiltered, full sunlight contains much more red light than far-red light. In practice, this means that plants begin to ‘power up’ around dawn – when there is more red light than far-red light – and then ‘power down’ down as the red light of the day begins to decay to far-red light through the night. During summer’s short nights there is not enough time for all the red light to fully decay to far-red and therefore a considerable amount of active proteins remain at dawn. Conversely, during winter when the nights are long, all the red light decays through the night, reverting all proteins to their dormant form by dawn. By sensing the active/dormant ratio of these proteins at dawn, a plant can determine the length of the day/night cycle.

So these phytochromes act like a plant’s watch – but amazingly, they also function as something like a diary. A plant’s leaves can retain and logo this ratio for several days. Shorter nights indicate springtime for the plant; when the nights become longer, autumn is approaching. 

At ample, we are distilling the knowledge of how plants react to different types of light to make growing your plants easy. Our user-friendly plant light will help you regulate day lengths in a way that reflects life’s natural rhythms, encouraging plants to grow the way nature intended.

Easy as flicking a switch.