What is the difference between a 500W high pressure mercury lamp and a 400W high pressure mercury lamp I know that the Wattage of a UV lamp is only one factor in the UV output of a light, and therefore cannot be used as a measure of how powerful a light is. Also it doesnt have any effect on the produced wavelength. Is it like this that a lamp with higher wattage can cause higher temperature on substrates that are being irradiated ?
I would say all other things being equal, i. e. Spectral distribution,  quantum efficiency,  that more wattage = more photons per second. And yes, more heat.