A UVA BL lamp with broad emission peak centered at 352 nm. The UVA intensity is 2.5 mW/cm^2 max and the lamp requires 4 AA batteries (not included). The figure below shows a plot of the relative UV irradiance emitted by one of these lamps at a distance of 1 cm as a function of time with 4 new AA Duracell batteries; a relative irradiance of 1 is equivalent to about 2.5mW/cm^2. This plot shows that typically new batteries would last for about 6 hours of continuous use. Note: After this period the lamp will still appears to be illuminated but the irradiance will be much lower than it should be.