An illumination system and method are disclosed for maintaining a consistent change in illumination value among a group of illumination devices whenever a change command is manually sent from a keypad to those illumination devices. The consistent change results from maintaining a common start illumination value among not only the group, but also the keypad which controls the group. From the start illumination value, the keypad can then compute an end illumination value depending upon the amount of time that an increase or decrease in illumination value button is depressed and held. Since the change command can arrive at different illumination devices within the group depending upon where each illumination device is geographically located, a masking time is reserved after the button is released so that enough time is allocated for each of the illumination devices within that group to arrive at a common end illumination value.