I can tell if i'm waking up at 7:00 in the morning not 7:00 in the evening.  I have done just that woke up at 8:00 pm and thought it was 8:00 am so got ready for the day - made my bed, washed my hair, showered, ate breakfast, got dressed for the day.  Once realizing my mistake, didn't want to go back to bed with wet hair, and then have to remake my bed.  This clock tells me if it is morning or evening and I can go right back to bed and sleep till a normal time to get up, if it was evening not morning.