For f.lux, no registration required (personal use). Lightbulb can be used for business use also, I guess.
I tried both of them, both have their own advantages. Flux uses half the memory then LightBulb and has more intuitive UI. LIghbulb on the other hand gives easy control, has less presets, configuration and saves the user settings in a single file, useful for people like me who need to copy settings to many computers.