What is Photosynthetically Active Radiation (PAR) – Types of Carbon


The amount of light available for photosynthesis of plants is called Photosynthetically Active Radiation (PAR) which is from of 400-700 nm in wave length. It is essential for photosynthesis and plant growth. PAR is not always constant because of clouds, tree shades, air, dust particles, seasons, latitudes and length of the daylight availability.

Generally plants absorb more blue and red light for efficient photosynthesis. Of the total sunlight, 34 percent that reaches the atmosphere is reflected back into the atmosphere, moreover 10% is held by ozone, water vapours and atmospheric gases and the remaining 56% reaches the earth’s surface. Out of this 56%, only 2 – 10% of the solar energy is used by green plants for photosynthesis while the remaining portion is dissipated as heat. PAR is generally expressed in millimoles / square meter / second by using silicon photo voltic detectors which detect only 400 – 700 nm wavelength of light. PAR values range from 0 to 3000 millimoles /square meter / second.

At night PAR is zero and during midday in the summer, PAR often reaches 2000 – 3000 millimoles /square meter/second.

Types of Carbon

Green carbon – carbon stored in the biosphere (by the process of photosynthesis). Grey carbon – carbon stored in fossil fuel (coal, oil and biogas deposits in the lithosphere). Blue carbon – carbon stored in the atmosphere and oceans. Brown carbon – carbon stored in industrialized forests (wood used in making commercial articles) Black carbon – carbon emitted from gas, diesel engine and coal fired power plants.

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