The meter shows the power of UVB and PUVA lamps.
The display is in mili watt.
You can use the lamp to test the power of UVB lamps.
To know the energy that is given to the skin, multiply the meter display by the exposure time seconds.
For example of the meter shows 2 and you used the lamp for 100 second it means that the skin got 2 X 100 = 200 mili joules.