Every light is worth a power of two. Add up the lit ones in a column and you have the digit. It feels impossible for about a minute, and then you can't stop reading it.
The time is
This is the layout most binary clocks use, called binary-coded decimal. Each of the six columns is one digit of HH:MM:SS. Rows are worth 8, 4, 2 and 1 from top to bottom. A column with the 4 and the 1 lit is a 5.
Some spots are missing on purpose. The first hour digit never goes past 2, and the first minute and second digits never go past 5, so they don't need the 8 (or the 4).
This is real binary: hours, minutes, and seconds each get one row, and the whole number is written in base two. The lights from right to left are worth 1, 2, 4, 8, 16 and 32.
Minutes and seconds need six lights because 59 is 111011. Hours only need five, since 23 is 10111.