The projection of a ceiling projection clock with high brightness can be seen during daytime and even when indoor areas are well-illuminated. However, the projection generated by projection clocks with low brightness can be seen only in a dark room.
A projection clock with low brightness contains a projector with a red LED backlight, whereas the high-brightness clock uses a halogen bulb.
However, a low-brightness projection clock can be seen during the daylight if it contains an ordinary LED light or an LCD display in addition to the red-LED backlight.
To make the display clear, the clock must be positioned between 18 inches and 12 feet from the ceiling.