A natural source of infrared radiation is sunlight. Approximately what percentage of average sunlight is infrared radiation as compared to ultraviolet radiation?

• A. 60%
• B. 50%
• C. 40%
• D. 70%

Answer: (A)

The amount of energy in infrared light is by far the largest part of sunlight that reaches Earth, while ultraviolet is a much smaller portion because the atmosphere absorbs much of it. In typical solar-spectrum estimates, infrared makes up roughly half to a little more than half of the energy—about 50–60%—whereas ultraviolet accounts for only around 5–10%. So infrared is the dominant component, and a rounded figure of about 60% is the closest match to how much infrared energy there is compared with ultraviolet. The other percentages would understate or overstate infrared’s share relative to ultraviolet.