For normal hot cathode mercury uv lamps , they are suggested to be replaced each year. This series uv lamps are widely used in air purifier.
And for amalgam uv lamp , they are suggested to be repalced each one year and a half.
And for cold cathode uv lamp, they are very long life , over 20,000 hours service life. They are usually widely used for some small products, such as toothbrush sanitizer, mini sterilizer, etc. If no damage, they do not need replacment each 5 years.