There are two types of non-electrical exit signs, photoluminescent (charges by absorbing light) and self-luminous which emit light from tritium gas filled tubes. There are strengths to using either but if you don't have consistent ambient lighting above 5 foot candles available to charge the photoluminescent sign it comes down to one choice, self luminous. Self luminous signs are available in two life spans, 10 years and 20 years, which means that you don't need to run wires nor provide any additional power in order for these lights to shine for 10 to 20 years. If you do have the required ambient lighting, typical in airports, hospitals, and residential building hallways, for example, then photoluminescent can be a great choice, especially for low level exit signs. See our FAQs on photoluminescent and self luminous exit signs down below the page.