## **Core Concept**
Ultraviolet (UV) radiation from the sun or artificial sources is categorized into three main types based on wavelength: UVA, UVB, and UVC. UVB radiation, in particular, is known for its role in causing sunburn and playing a key role in vitamin D synthesis in the skin. The wavelengths of UVB range is critical for understanding its effects on human health.

## **Why the Correct Answer is Right**
The correct answer, **290-320 nm**, corresponds to the UVB range. UVB radiation has a shorter wavelength compared to UVA but a longer wavelength than UVC. The specific range of 290-320 nm is crucial because it is primarily responsible for causing sunburn and is also the range that induces the synthesis of vitamin D in the skin. This range is partially absorbed by the Earth's atmosphere, particularly by the ozone layer, but enough reaches the Earth's surface to have significant health impacts.

## **Why Each Wrong Option is Incorrect**
- **Option A:** *100-200 nm* - This range is actually characteristic of UVC, which is almost entirely absorbed by the Earth's ozone layer and does not reach the surface.
- **Option B:** *320-400 nm* - This range corresponds to UVA, which has a longer wavelength than UVB and is more associated with skin aging and less with vitamin D synthesis.
- **Option D:** *400-800 nm* - This range is actually within the visible light spectrum and does not correspond to UV radiation.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that UVB radiation, with its wavelength of **290-320 nm**, is crucial for vitamin D synthesis but also poses a risk for sunburn and skin damage. Public health advice often focuses on balancing sun exposure to minimize risks while allowing for adequate vitamin D production.

## **Correct Answer:** . **290-320 nm**