Philips Back Up Light Bulb - 921B2: Philips 921B2 Back Up Light Bulb is a long-lasting, energy-efficient light bulb that provides a bright, white light. It is ideal for use in areas where you need a reliable source of light, such as hallways, stairwells, and other areas that require a backup light source. The bulb is designed to last up to 10 years, so you can count on it to provide reliable illumination whenever you need it.