Most of the upper end, high power lightbars have a low output mode for nighttime. Its up to the officer (plow driver, ambulance etc) to select it over the other power modes. Sounds like officers in some areas are selecting daytime power for night either "just because" or they feel, incorrectly, that maximum brightness increases safety when I remember reading reports that it is exactly the opposite. The dazzle effect at night is very strong with these high power, high speed flashers, arguably causing more risk to the officers.
Most RCMP here seem to select the correct power setting for nighttime, thankfully.
Modern lightbars and controllers are pretty computerized, youd think it would be easy for them to add a photocell to determine ambient light level and adjust output accordingly, unless running max power at night is SOP for some departments which is a bad idea IMHO.