**Core Concept**
A Wood's lamp is a diagnostic tool that emits ultraviolet (UV) light to visualize certain skin and mucous membrane lesions, such as vitiligo or fungal infections. The lamp's composition plays a crucial role in its ability to produce UV radiation.

**Why the Correct Answer is Right**
The correct composition of a Wood's lamp involves a specific ratio of nickel oxide to barium silicate, which allows it to produce a narrow range of UV radiation, typically in the 365 nanometer range. This specific wavelength is essential for visualizing certain skin lesions. The 9% nickel oxide with barium silicate combination enables the lamp to emit this specific wavelength, making it suitable for diagnostic purposes.

**Why Each Wrong Option is Incorrect**
**Option A:** The 9% nickel oxide with 6% barium silicate combination does not produce the desired UV radiation wavelength for diagnostic purposes.
**Option B:** The 9% nickel oxide with 9% barium silicate combination is not the correct ratio for producing the necessary UV radiation.
**Option C:** The 6% nickel oxide with 6% barium silicate combination is not sufficient to produce the desired UV radiation wavelength.

**Clinical Pearl / High-Yield Fact**
A Wood's lamp is a valuable diagnostic tool in dermatology, but it is not suitable for all skin conditions. The specific composition of the lamp is critical for its diagnostic capabilities, and incorrect combinations can lead to inaccurate results.

**✓ Correct Answer: D. 9% nickel oxide with barium silicate**