UVB germicidal lamps are primarily used in medical and scientific applications for the treatment of certain skin conditions such as psoriasis (psoriasis) and certain types of eczema. Both wavelengths (311nm and 308nm) of UVB light have their own specific application scenarios.

311nm UVB: This wavelength of UVB light is known as narrowband UVB (NB-UVB) and is a commonly used phototherapy treatment for psoriasis and other skin conditions. It promotes normalization of skin cell growth and reduces inflammation. Typically, 311nm UVB phototherapy is considered a relatively safe and effective treatment with fewer side effects. 

308nm UVB:The 308nm wavelength of UVB light is usually emitted through an excimer laser or handheld device. This wavelength is particularly suitable for localized treatments such as small psoriasis patches or vitiligo patches. 308nm UVB light is thought to be able to penetrate the top layers of the skin more effectively, treating specific areas while minimizing the impact on surrounding healthy skin. 

If you require full body phototherapy, a 311nm UVB light is usually chosen. If you only need to treat a specific small area of skin lesions, a 308nm UVB device may be more appropriate.