Figure 2-28. Portable 100-Watt Black Light.
A cross section of a typical mercury vapor arc discharge bulb is shown in Figure 2-29. The high pressure component is
a quartz tube containing some mercury plus a small amount of neon gas. When the lamp is first turned on, the mercury
is condensed as a liquid and an arc between the electrodes cannot be generated. This is the reason for the neon gas. A
small amount of current, limited by the resistor, causes a discharge from the starting electrode through the neon gas.
This glow is sufficient to vaporize the mercury, which then allows the arc to pass between the main electrodes. This
starting procedure requires from 5 to 15 minutes to fully vaporize the mercury and produce full output of black light.
Some blacklights may be warmed-up in 2-3 minutes. Refer to the owners manual the light you are using. Black lights
SHALL NOT be used for inspection before the required intensity at the inspection surface (paragraph 220.127.116.11.5) is
Figure 2-29. Cross-Section of a Typical High Pressure, Mercury Vapor Arc Bulb.