ut is does tell you whether it's day or night:
The Day&Night is graced with the first Romain Jerome movement, the ‘RJ One’ movement developed exclusively for RJ by BNB Concept.
I imagine this would be THE watch for a blind person who can't tell if it's dark and has to ask what time it is.
My watch does tell me the sunrise and sunset times - and it uses the WWVB time signal from Colorado to synchronise with the Atomic Clock. It's also solar powered to eliminate the tedious battery changes every 4 years. As you can tell I'm a bit of a geek.
My eldest son however is a total geek and proud of it, so he has a binary watch. He's got pretty good at reading it, I can but it takes me too long.