**Core Concept**
The Wood's lamp is a diagnostic tool used to visualize certain skin conditions, particularly those caused by fungal or bacterial infections. It emits ultraviolet (UV) light, which causes fluorescent reactions in affected areas, allowing for easier diagnosis.

**Why the Correct Answer is Right**
The Wood's lamp emits UV light at a specific wavelength of 365 nanometers (nm), which is within the UVA spectrum. This wavelength is chosen because it is effective in exciting certain fluorescent compounds, such as porphyrins, in microorganisms like Pityrosporum ovale, which causes pityriasis versicolor. When exposed to 365 nm UV light, these compounds emit longer-wavelength light that is visible to the human eye, allowing for the detection of infected areas.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the Wood's lamp does not emit UV light at a wavelength of 254 nm, which is typically used in disinfection and sterilization procedures.
* **Option B:** This option is incorrect because the Wood's lamp does not emit UV light at a wavelength of 450 nm, which is in the blue-violet region of the visible spectrum and not typically used for diagnostic purposes.
* **Option C:** This option is incorrect because the Wood's lamp does not emit UV light at a wavelength of 100 nm, which is in the vacuum ultraviolet region and not typically used for medical diagnostics.

**Clinical Pearl / High-Yield Fact**
The Wood's lamp is a simple and non-invasive tool that can be used to diagnose a range of skin conditions, including fungal infections, bacterial infections, and certain types of acne. It is an essential tool in the dermatologist's arsenal and can be used in conjunction with other diagnostic techniques to aid in accurate diagnosis and treatment.

**Correct Answer: C. 365 nm**