## **Core Concept**
A Wood's lamp is a diagnostic tool used in dermatology to aid in the diagnosis of various skin conditions. It emits ultraviolet (UV) light, which helps in identifying certain skin disorders based on the characteristic fluorescence or changes in skin lesions under UV illumination. The conditions diagnosed using a Wood's lamp include fungal and bacterial infections, vitiligo, and porphyrias.

## **Why the Correct Answer is Right**
The correct answer involves conditions that exhibit characteristic changes under UV light from a Wood's lamp.
- **Vitiligo (b)**: Shows blue-white fluorescence due to the absence of melanin.
- **Porphyria (c)**: Exhibits pink or purple fluorescence due to the accumulation of porphyrins.
- Other conditions like **P. versicolor (a)** caused by Malassezia yeast, shows a yellowish-green fluorescence.

## **Why Each Wrong Option is Incorrect**
- **Option A: Psoriasis (d)**: While psoriasis is a common skin condition, it does not typically exhibit a specific diagnostic fluorescence under a Wood's lamp.
- **Option B: Lichen planus (e)**: Lichen planus does not have a characteristic fluorescence under UV light; its diagnosis is primarily clinical and histopathological.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that a Wood's lamp can help differentiate between various causes of skin lesions, particularly in cases of suspected fungal infections (like ringworm) which show a bright green fluorescence, and vitiligo.

## **Correct Answer: B. Vitiligo, Porphyria.**