Photobiology, Blinking and Far-Red Light to Increase Vegetable Yields

By: Rocco Brewer,

June 25th, 2017.

The Role of Light:

The word "light" is often defined as what is perceived by the human eye. More precisely, light is the wavelengths in the electromagnetic spectrum that activate light receptors in the human eye. However, plants respond to all the wavelengths of the electromagnetic spectrum. These include the wavelengths that the human eye can (visible light) and cannot see (ultra-violet and infra-red light). So Far Red is dimly visible to some eyes.

Far-Red light is the light of dusk and dawn. It sits at the extreme red end of the visible spectrum, between red and infra-red light. Usually between 700 and 800 nm wavelength.

Light in human or animal vision acts mainly as an informational medium to distinguish the location, movement, shape, size, color and other aspects of material objects. Plants use light for a similar purpose in that variations in light can signal variations in environmental conditions surrounding the plant. Photo-receptors within plants function as light sensors that provide plants with information on subtle changes in light composition in the growing environment, and also control physiological and morphological responses. This process is technically known as photo-morphogenesis. It guides the plant to direct its growth pattern to reach for the source of illumination.

However plants also use light for the production of food through photosynthesis. We know this to be the process by which plants convert carbon dioxide and water into carbohydrates and oxygen (in the presence of light).

In Plant growth and development, the most important regions of the light spectrum can are listed below.

ultra-violet (below 400 nm)

visible (approximately 400-700 nm)

far-red (approximately 700-800 nm).

Grower Applications of Photo-morphogenesis

The effects of far-red light have generally not been used in growing giant vegetables. Environments high in far-red light are favorable for the production of plants that need Cell Elongation, Long Inter-nodes & Enhanced Cell Division. Therefore, an increase in far-red light in the patch or greenhouse could be used to increase steam lengths, leaf size and yes larger fruit.

In the patch or greenhouse, light quality manipulation can be achieved in three ways:

Ø Supplemental electric lighting systems with relatively high far-red light.

Ø Reflective materials, or red plastic mulch layers or red bark mulch

Ø Spectral filters that can alter the red and far-red balance of sunlight.

Incandescent Lamps

• Growers to USE Regular Incandescent bulbs

High levels of far-red light relative to red light frequently lead to cell elongation and increased inter-node lengths leading to leaf growth rates & canopy leaf expansion, stem elongation and fruit cell expansion. Typical light quality of white fluorescent lamps. Does not provide enough Far-red Light, so they produce short, compact plants.

1. Blinking at 1 am each night. Interrupts the photo period. For Blinking use broad spectrum light to as much of the plants as possible to interrupt the photo period and drive night time growth. Blink for 3 to 5 minutes

2. Use Far Red light in the morning from 4 am to 6 am and 9:30 pm to 11 pm.