Don's bulbs rare light bulbs and lamps glossary of terms definition of: DARK-EFFECT What is DARK-EFFECT? With glow lamps, external ion energy (like light particles) interferes with (lowers) the Breakdown Voltage point, so if the Glow Lamp is energized were no outside ion influence the bulb (like a dark room), much more voltage is then required to hit the Breakdown Voltage point and this phenomena is called dark-effect. To prevent dark-effect some glow lamps include a small amount of radioactive gas (krypton 85) which stabilizes break-down voltage regardless of external ion influences. reference for this page: DARK-EFFECT reference to this page: GLOW LAMP