Irradiance.

Irradiance is radiant power arriving at a surface per unit area, W/cm² or mW/cm², and it is a different measurement from the mJ/cm² figure most cure specs quote. RadTech's UV glossary defines energy density as the time integral of irradiance, which is why belt speed and lamp strength trade against each other to hit the same energy number, while peak irradiance, the maximum of the profile directly under the lamp, does not trade at all. The same glossary is blunt about two habits on the floor: dose is borrowed from electron beam work, where it means energy absorbed per unit mass, and a tubular lamp described in watts per inch is quoting electrical input divided by bulb length, which says nothing about the UV that reaches the work. Neither figure means anything without the wavelength band it was measured in, and neither means anything measured somewhere other than the surface being cured. A line that keeps hitting its energy target on a failing lamp cures a skin over soft ink, and that ships before anybody reads it.