Q.How much percentage of photo-synthetically active radiation is captured by plants?
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Imagine you are standing in a sunlit garden. You feel the warmth of sunlight on your skin, and you can see the bright green of the leaves. But here is the key: the plant does not use all that sunlight for its food-making process. It is picky. It only uses a specific slice of the sunlight — the part that is "photosynthetically active."
That specific slice is called Photosynthetically Active Radiation, or PAR for short.
The Precise Meaning
Sunlight is a mixture of different colours (wavelengths), from violet and blue to green, yellow, orange, and red. Plants have a pigment called chlorophyll that captures light energy. But chlorophyll does not absorb every colour equally. It absorbs light most strongly in the blue and red regions of the spectrum. It reflects green light — that is why leaves look green to us.
Photosynthetically Active Radiation is simply the portion of the light spectrum that plants can actually use for photosynthesis. In scientific terms, it covers the wavelength range from about 400 to 700 nanometres. This range includes blue light, red light, and everything in between — but it excludes ultraviolet (shorter than 400 nm) and far-red/infrared (longer than 700 nm).
PAR is not a measure of how much light there is in total. It is a measure of how much usable light is available for photosynthesis. A dim, red-lit room might have high PAR, while a bright, green-lit room might have low PAR — because plants cannot use green light well.
Why It Matters (Even for a Humanities Student)
You might wonder: why should a commerce or humanities student care about a technical term from plant biology? Here is why.
- Agriculture and food security: Farmers and agronomists measure PAR to know if crops are getting enough usable light. If a crop is shaded by a building or a taller plant, the PAR drops, and yield falls. This directly affects food prices and supply chains — something a commerce student studies.
- Climate and environment: PAR is a key input in models that predict how much carbon dioxide forests and oceans absorb. This links to climate change, which affects everything from insurance premiums to migration patterns — topics a humanities student encounters.
- Urban planning and architecture: When designing green buildings or vertical gardens, architects must ensure enough PAR reaches the plants. A poorly lit indoor garden will fail, no matter how beautiful the design.
PAR is not the same as total sunlight. A cloudy day may still have high PAR if the clouds are thin, while a bright sunny day may have low PAR if the sun is low in the sky (more red/infrared, less blue). Always think: usable light, not visible light.
What the NCERT Textbook Says
The NCERT Class 11 Biology textbook (Chapter 13: Photosynthesis in Higher Plants) states clearly: …
Not all of the sunlight reaching a plant is usable for photosynthesis, and even the usable (photosynthetically active) portion is only partly captured and converted by the plant. …
Of the incoming PAR, plants convert only about 2-10% into chemical energy through photosynthesis.
Less than half of the incident solar radiation is photosynthetically active radiation (PAR), and of this PAR the plants (producers) actually capture and fix only a small fraction — roughly 2 to 10% — int …
- CBSE 2026Set A1 markMCQQ.How much percentage of photo-synthetically active radiation is captured by plants?(a) 50%(b) 2-10%(c) 10%(d) 20%
›Reveal solutionSolution
Of the incoming PAR, plants convert only about 2-10% into chemical energy through photosynthesis.
Less than half of the incident solar radiation is photosynthetically active radiation (PAR), and of this PAR the plants (producers) actually capture and fix only a small fraction — roughly 2 to 10% — int …
- CBSE 2026Set ANNUAL1 markMCQQ.What is the percentage of photosynthetically active radiation (PAR) captured by plants for the synthesis of organic matters?(a) 100%(b) 50%(c) 1 - 5%(d) 2 - 10%
›Reveal solutionSolution
Although the sun provides abundant radiation, plants are able to fix only a small fraction (about 2-10%) of the photosynthetically active radiation (PAR) into chemical energy via photosynthesis.
Of the total solar radiation reaching Earth, less than 50% falls in the 400-700 nm wavelength range usable for photosynthesis — this usable portion is called Photosynthetically Active Radiation (PAR). However, plants do not efficiently use even all of the PAR that reaches them; a substantial fraction is reflected, transmitted, or lost as heat.
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- CBSE 2025Set ANNUAL1 markMCQQ.What is the percentage of the photosynthetically active radiation (PAR) in the incident solar radiation?(a) 100%(b) 50%(c) 1 - 5%(d) 2 - 10%
›Reveal solutionSolution
Of all the solar radiation striking the Earth, roughly 50% falls in the wavelength range (about 400-700 nm) usable by plants for photosynthesis - this fraction is called PAR.
Sunlight reaching the Earth's surface spans a wide range of wavelengths, but only the visible-light portion (roughly 400-700 nm) can be absorbed by chlorophyll and other photosynthetic pigments and used to drive photosynthesis; this usable fraction is called photosynthetically active radiation (PAR), and it constitutes about 50% of the total incident solar radiation. It is important not to confuse this with the SEPARATE, much small …
- CBSE 2024Set ANNUAL1 markMCQQ.What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation?(a) 10%(b) 25%(c) 50%(d) 100%
›Reveal solutionSolution
Of all the sunlight that reaches Earth, only about 50% falls within the wavelength range (roughly 400-700 nm) that plants can use for photosynthesis - this fraction is called PAR.
Of the incident solar radiation, much is reflected back to space, absorbed by the atmosphere, or falls outside the wavelengths chlorophyll can use. Photosynthetically Active Radiation (PAR) refers only to the visible-light band usable for photosynthesis, …
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