Answer : My recommendation is a hitherto-little known gem, called ScreenShade. There are several decent Mac software screen dimmers out there, of which I've found the ones whose dimming method is to apply an increasingly opaque black 'overlay' over the screen to be the most superior in appearance (providing much higher quality 'low blacks' than Shades which does its dimming via color profile/gamma level tweaking) and in doing so, also playing nice with famous color temperature regulating app, f.lux. The best examples in this group, are Shady (whose development has been abandoned by its dev and has a no better rogue clone in the Mac App Store), ScreenDimmer, Screen Shade, and Work at Night. (N.b. these last two, confusingly appear to be clones, by the same dev on the Mac App Store.) But if you're looking to more fully emulate the Mac's in-built hardware dimming in software, you're looking for an app that can have the dimming triggered via hotkey...