How Different Spectra of Light Affect Plant Growth

It is a fact that plants are dependent on light to generate food, grow and reproduce. Without light the process of photosynthesis will not take place and natural growth cycle will not occur. When a plant is under natural lighting conditions, its growth and development is influenced by the sunlight it receives which is dependent on season and other environmental factors. Natural light consists of different wavelengths and color spectrums. They vary in wavelength, characteristics, and effect plants differently during various stages of their life cycle. Not all wavelengths present in natural sun light are used in photosynthesis process. In general, when color and wavelength are considered, each will have a specific effect on plants. Let’s us look at different spectral compositions of light:

Ultraviolet

UV lights are lights with wavelength between 100nm – 400nm. They contain excess amounts of energy that can damage plant cells if not used properly. Though the far end radiation nearer to 400nm are helpful in some aspects of plant development, exposing them too much to UV light can affect the photosynthesis rate, slowdown the growth process or even damage the seed development.

Infrared

Infrared light has much longer wavelengths, outside the visible spectrum which a human eye cannot detect. Since infrared has wavelengths beyond visible spectrum i.e. between 700 nm - 3000 nm, their energy cannot excite the plant cells for photosynthesis. Though appropriate levels help in flowering and stem growth, too much of infrared light particularly the far red end of the spectrum eventually damage the plant because of the excess heat. Infrared light either make the plants long stemmed or encourages them to bloom early.

Visible light

Visible light includes electromagnetic radiation between wavelengths 400nm to 700nm. The visible spectrum is made of multiple wavelengths with different colors, containing photosynthetic active radiation (PAR) that is effective in photosynthesis process. Only specific wavelengths from visible light are absorbed by plant cells whereas wavelengths that are not absorbed are reflected or transmitted. For instance the wavelengths of blue and red from the spectra of visible light are most absorbed by the plants whereas green is not absorbed but reflected back because the plants themselves are green due to the pigment Chlorophyll.

What a full spectrum light includes?

Full spectrum includes wavelengths in the visible range along with other invisible spectra such as ultraviolet and infrared. Full spectrum lights which are typically used by gardeners for indoor farming replicate natural solar spectrum with wavelengths corresponding to different colors. Mostly, gardeners rely on LEDs because they are very effective in producing full spectrum radiation. LEDs are able to tailor the wavelengths specific to the needs of crops. By varying the color and spectral outputs, the physical properties of plants can be controlled at various stages of cultivation.

Effect of each color on plants

Each color in visible light is important and contributes for growth of plants. Of the entire electromagnetic spectrum, blue and red wavelengths are most effective in photosynthesis. For example, blue helps in vegetative leaf growth, whereas, red light combined with blue, helps plant to flower. Green and yellow lights are less effective compared to other colors but are still invaluable to natural plant growth. Violet enhance certain specific plant characteristics such taste & aroma. This way each spectra of the light has a prime importance in plant growth and development.

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