Mercury depletion as a way of changing the emission spectrum of a fluorescent lamp

We present a promising option for changing the emission spectrum of a fluorescent lamp. In a neon/mercury discharge, neon radiation is produced when the mercury density is sufficiently low. Under certain discharge conditions, radial cathaphoresis causes depletion of mercury atoms in the center of the plasma. This effect is especially well pronounced at high electrical currents and low mercury pressures. We measured the color temperature of a fluorescent lamp containing a neon/mercury discharge at several mercury pressures and currents. The color temperature of this lamp varied from 4000 to 2100 K. We also performed ultraviolet absorption measurements. From these measurements, we obtained the mercury atom density profile in the discharge. A significant decrease of the mercury density in the center of the plasma is indeed observed under certain discharge conditions.