Question

Direct solar radiation contains how much PAR?

• A. 30%
• B. 50%
• C. 42%
• D. 65%

Hint:

Direct sunlight has a lower PAR percentage (\(\approx\) 42 %) compared to cloudy, diffuse daylight (\(\approx\) 60-70 % PAR) because clouds selectively filter out infrared wavelengths.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Photosynthetically Active Radiation (PAR) designates the spectral waveband of solar radiation from 400 to 700 nm, which is absorbed by photosynthetic pigments.

Step 3: Detailed Explanation:
Incoming solar radiation is split into direct solar beam radiation and diffuse sky radiation (scattered by clouds and atmospheric particles).
1. Under clear sky conditions, direct solar radiation contains approximately 42 % to 45 % PAR, with the remaining percentage falling in the ultraviolet and infrared spectra.
2. Diffuse sky radiation has a higher proportion of shorter wavelengths due to Rayleigh scattering, containing a much higher percentage of PAR (up to 60 % to 70 %).
Thus, the direct solar radiation fraction contains about 42 % PAR.

Step 4: Final Answer:
The correct option is 3, which corresponds to 42%.