Light metering: Red / Far-Red

The light is the engine of plant growth and the red/red-leaf ratio is a fundamental pillar of its development.

Its self-sufficiency in matters of nutrition is still astounding to this day. Few ingredients are needed for plant life to develop normally. But light is not only used for food. They also receive other stimuli from light that are really important for their development.

Plants develop on the basis of the spectrum of light they receive.

Plants absorb red light (660-680 nm) and reflect far-red light (720-740 nm). The photoreceptors that control the physiological developmentare called phytochromes. These phytochromes react to fluctuations in red and far-red light levels.

The far red causes weak growth and desperate movements of the plants to look for intense light.

The most significant responses to the red - far-red relationship are:

• Seed germination
  • Sowing, weeds...
• Stem elongation
  • When the far red levels are high it means that there is little direct light so the plant needs to stretch out in search of light intensity.
• Flowering
  • This ratio determines the time of flowering.
• Gene expression
  • Development of crop-specific characteristics
• Development of more vegetation cover and a higher concentration of chloroplasts.

The leaf tissues act as a filter by letting more far-red light through than red light. This changes the ratio of red to far-red light coming from the sun. This phenomenon occurs in plants with many leaves, causing those that do not receive direct light to have a low ratio of red to far-red or when the density of plants is high and they block each other.

Knowing the red-to-far-red ratio helps determine plant spacing and determines key times to apply growth regulators. By making precise applications of the regulators and having the right spacing, advantages such as more uniform, bushy growth or larger fruits are achieved.

The quality of the plant depends on the quality of the light (spectral composition). A light with too much far red is poor in terms of growth.

In the words of Peggy McMahon, associate professor in the department of horticulture and crop science at Ohio State University. Far-red light plays a critical role in plant growth. It is an important factor in promoting the shade avoidance response (elongation and stretching of stems) in plants. Far red cannot be detected with the naked eye, so having a meter that allows us to know how much red and far red light (antagonistic in their effects) the plants are receiving, especially that which hits the leaf beam is very useful. The meter can help the grower to space the plants or maintain a suitable height so that the plants have the space they need and at the same time do not waste space.