big LED matrix, 32 x 24 LEDs

"No, I drive 32 Columns at once, but only activate one from 6 rows."
"For 24 rows, 4 rows are active at any time."

So, at most 24 LEDs could be on at one time?

Okay, so 4 * 6 * 20mA (max current on most LEDs) = 480mA