A glow switch starter is a type of preheat starter used with fluorescent lamp. The common fluorescent lamp relies on fluorescence. Bimetal strips are also used in time-delay relays, lamp flashers, and fluorescent lamp starters. Simple inductive fluorescent lamp ballasts have a power factor of less than unity. The compact fluorescent lamp (CFL) is becoming more popular. However, Shabbat lamps are lit by and only accept a compact fluorescent lamp. According to the Northwest Compact Fluorescent Lamp Recycling Project, because household users in the U.S. PCB-filled paper capacitors are found in very old (pre-1975) fluorescent lamp ballasts, and other applications. The fluorescent lamp first became common in the late 1930s. Dried semen that is on clothing and skin can be detected with a fluorescent lamp. A fluorescent lamp converts electrical energy into useful light much more efficiently than incandescent lamps. In 2009, the incandescent light bulbs were replaced with energy- and money-saving fluorescent lamp fixtures. The common fluorescent lamp is a low-pressure mercury arc lamp. PCB-filled capacitors are found in very old (pre 1975) fluorescent lamp ballasts, and other applications. A small discharge lamp containing a bi-metallic switch is used to start a fluorescent lamp.