I've owned three of these units. A unit of light is not equal to a second. Although you can adjust them to be close to a second. But there is really no need to. Just develop your work flow in units and forget about seconds. You will notice the integrator runs slow on start up and will increase in speed as the unit warms up and the light intensity increases. But if your heart is set on knowing how many seconds then by all means start adjusting your photocell until to you have it set on one second equals one unit.