Visible Spectrum of Light

 The term photo-physiology refers to the study of physiological reactions as influenced

by light. Light influences various physiological processes directly or indirectly like photosynthesis, flowering

phenomena(photoperiodism), phototropism, chlorophyll synthesis, seed germination, protoplasmic

streaming, etc.

Visible Spectrum of Light

* Sun is the ultimate and huge source of light energy. The earth intercepts very little amount of

this energy.

* The so-called light is the visible part of the spectrum of electromagnetic radiation.

` It ranges from 380 to 760.

* A white light consists of violet (390-430nm), blue (430-470nm), blue-green (470-500nm),

green(500-560nm), yellow(560-600nm), orange (600-650nm), and red(650-76nm).

* But, there are several physiological processes, which are affected by 280 to 800 nm of which, the

wavelength of light ranging from 400to 700 nm is very efficient in increasing the rate of

photosynthesis. This range of wavelength (400-700nm) of the visible spectrum of light is

called Photosynthetically Active Radiation (PAR)

* Light travels in the form of a stream of discrete particles called Photos, which contain a packet of `

energy called Quantum.

* It is considered that the longer wavelength of light will possess lesser energy while the shorter wavelength will have a greater energy level.

A Summary of light affected processes are given below :

S.No.                      Wavelength (nm)                          Band                                   Process

1.                               280nm and below                     x and γ       This region is lethal and is absorbed by

                                                                                                           nucleic acid cosmic rays.

2.                               280 to 400                                UV rays        It induces rosette growth and thick                                                                                                                                 leaves in plants.

3.                               400to 510                                 Blue          It actively influences photosynthesis and

                                                                                            accelerates phototropism. It is blue light and is

                                                                                                absorbed by carotenoids, flavoproteins,

                                                                                                                phytochrome, etc.

4.                           510to 610                             Green              In this region, the least amount of                                                                                                                           photosynthesis

                                                                                                and (yellow) morphogenesis are found

5.                           610to700                            Orange      This is the most active zone of light useful to

                                                                                   & Red plants in which the highest rate & amount of

                                                                                        photosynthesis is observed. Pollen and seed

                                                                                         germination and flowering are remarkably

                                                                                           influenced. Pr form of phytochrome

                                                                                                        absorbs this light.

6.                             700 to 800             Infra-red       This range of light is utilized by bacterio-chloro

                                                                                               phyllo to carry on bacterial photosynthesis.

                                                                                          For the form of phytochrome absorbs this light.

                                                                                                Elongation of internodes occurs.