by interruption of the electric supply), it is not possible for the lamp to restrike until the bulb cools enough for the pressure to fall considerably. The reason for a prolonged period of time before the lamp restrikes is to due the elevated pressure, which leads to higher breakdown voltage of the gas inside (voltage needed to start an arc – Paschen's law), which is outside the capabilities of the ballast. Color considerations To correct the bluish tinge, many mercury vapor lamps are coated on the inside of the outer bulb with a phosphor that converts some portion of the ultraviolet emissions into red light. This helps to fill in the otherwise very-deficient red end of the electromagnetic spectrum. These lamps are generally called "color corrected" lamps. Most modern mercury vapor lamps have this coating. One of the original complaints against mercury lights was they tended to make people look like "bloodless corpses" because of the lack of light from the red end of the spectrum. A common method of correcting this problem before phosphors were used was to operate the mercury lamp in conjunction with an incandescent lamp. There is also an increase in red color (e.g., due to the continuous radiation) in ultra-high-pressure mercury vapor lamps (usually greater than 200 atm.), which has found application in modern media projectors. When outside, coated or color corrected lamps can usually be identified by a blue "halo" around the light being given off. Emission line spectrum The strongest peaks of the emission line spectrum are In low-pressure mercury-vapor lamps only the lines at 184 nm and 254 nm are present. Fused silica is used in the manufacturing to keep the 184 nm light from being absorbed. In medium-pressure mercury-vapor lamps, the lines from 200 to 600 nm are present. The lamps can be constructed to emit primarily in the UV-A (around 400 nm) or UV-C (around 250 nm). High-pressure mercury-vapor lamps are commonly used for general lighting purposes. They emit primarily in the blue and green. Ultraviolet cleaning Low-pressure mercury-vapor lamps usually have a quartz bulb in order to allow the transmission of short wavelength light. If synthetic quartz is used, then the transparency of the quartz is increased further and an emission line at 185 nm is observed also. Such a lamp can then be used for ultraviolet germicidal irradiation. The 185 nm line will create ozone in an oxygen