photosensitive

Photosensitive describes anything that responds to light exposure. In science, it refers to properties of substances, materials, or organisms whose chemical, electronic, or biological state changes when illuminated. Photosensitivity depends on the wavelength and intensity of light, and on the material’s electronic structure or photochemical pathways.

In materials science, photosensitive materials produce photogenerated charge carriers or undergo reversible color or phase changes when exposed to light. Applications include photoconductors in detectors, photoresists used in semiconductor lithography, and solar cells that convert light into electricity. Photochromic compounds and lenses darken or lighten in response to light.

In biology and vision, photoreceptor molecules such as rhodopsin in rods and opsins in cones absorb light, triggering signaling cascades that enable sight. Other organisms use photosensitive proteins to regulate circadian rhythms or movement toward light (phototaxis).

In medicine and safety, photosensitivity describes increased sensitivity to sunlight. Certain drugs (for example, some antibiotics and antifungals), herbal supplements, and skin conditions can cause photodermatoses, sunburn-like reactions, or exaggerated tanning. Photosensitive epilepsy is a neurological condition where flickering or flashing lights provoke seizures in some individuals.

Industrially, handling photosensitive materials requires careful light management, appropriate storage, and often dark or inert environments to prevent unintended exposure during synthesis, processing, or storage.