I simply use a blue lamp.I have a twin light with one marine lamp and one daylight lamp.Then I have a separate single light with a blue lamp.Both are on timers.The blue light comes on at 14:00 for 1 hour.the marine and daylight come on at 14:45 so they overlap.The blue light comes on again at 20:00 until 21:00 and the marine and daylight go off at 20:15
I prefer it this way so it eases the fish in and out of light.