This is a daylight protection feature of the SPL III (Daylight lamps burn very hot and this feature extends their life). There will be an asterisk (*) in the display window next to Daylight. To turn this feature off, simply depress the Daylight button one more time. The asterisk (*) will disappear signifying the feature has been disabled.
Note: This feature is set as a default every time the SPL III is turned on.