@zekeflash,

If your outbuilding light works the way I think it does, where it measures the amount of light in the environment and emits a specific amount of light based on it, then I would assume that the light would simply recalculate when given power.

The KP400 will work as if you had the light attached to a light switch, as it simply cuts the power being fed to the switch. I assume that this is a typical use case for your light and would have been accounted for, but the only way to verify is through testing.