You would, at minimum, download a lux meter app to your smartphone, and use that to balance the intensity of the new setup with the intensity of the old setup.
There should be minimal difference in intensity when you switch. Wait a few months before making any other changes.
Remember: more light usually isn't better unless "more" = more coverage. Don't assume you have to turn it up unless you are under 30,000 lux and want clams. That's their minimum, so you may eventually want more like 40,000-50,000 lux at the surface.
These apps use the camera's light meter to compute a regular lux reading. Fine for the cost – $free. :)
For $15, delivered, it makes a lot of sense to look up something like the "LX-1010B" lux meter....it's a handheld with a remote sensor. Much safer to use over your tank and better readings than the app.
Recently, someone even used the LX-1010B's sensor underwater a few times and it seemed to give believable readings....not sure what that does for the longevity of the wiring and sensor, but at $15, maybe that's a small concern. I'd rinse mine really well in RODI water after submersed use. (I only take readings above water and do fine with only that info.)
