The direction the "1" on the light die is facing is the direction of the corridor the door is blocking (including up or down).
The direction the "1" on the dark die is facing is the direction to the trigger for the door.
If both dice come up even, the door is unlocked.
If one die comes up even and the other odd, then the door is locked.
If both dice come up odd, the door is stuck.
If the total of the die roll is 7, the door is trapped.
If you roll doubles, the door is already opened (it may be stuck open).
This does mean all upwards-pointing doors will be either stuck or locked but never unlocked, and all downwards facing doors will either be unlocked or locked, but never stuck. I also use it so that the orientation of the door follows the orientation of the die, so if it's oriented in a diamond shape instead of a square, the door is also set in a diamond shape instead of a square.