Premium Quartz series is a range of night glow clock which have an ability's to glow and show the time in the dark. The duration of glow depends on the time the clock has been exposed to any source of light (be it sunlight or any other form of light)the more light it absorbs in the day, the more it emits in the dark. 9br Quartz is absolutely safe for human eye & the environment sice it does not contain any carcinogenic inks or paints. Every glow are the only clocks which have the ability to glow throughout the night bringing a cheerful morning to you.