You have to have circuitry that allows you to control current flow through every LED individually. You can activate them one at a time or you can activate them in rows or columns, or whatever, but you MUST control the amount of current flowing in each LED segment individually at all times. If you multiplex them, you have to ensure that there's enough current to make them adequately bright. If you do that, you must also ensure that they're on long enough that people notice.

RE