A binary clock is usually a clock which displays traditional sexagesimal time in a binary format. With BCD Binary Clocks (the most common ones), to read each individual digit in the time, the user adds the values that each illuminated LED represents, then reads these from left to right. The first two columns represent the hour, the next two represent the minute and the last two represent the second.
Binary BCD Clock
How to read the time: add the values of each column of LEDs to get six decimal digits. There are two columns each for hours, minutes and seconds.