High pressure sodium lights are used for illuminating large outdoor areas. They emit bright yellow light. Typically these lights are used on sides of industrial buildings and in some street lamps. Sodium bulbs can last up to 20,000 hours. The heavy duty transformer or ballast is also long lived if the bulbs are changed out before they burn out. These lights are typically controlled by a photocell that turns the light on at dusk.
The most common problem with a high pressure sodium light is the bulb. The first course of action is to simply change the bulb. Observe the interior gas tube for any signs of discoloration. If the tube is black, the bulb is definitely burned out. Check the porcelain holder for any signs of deep cracks or breaks. Look inside the porcelain holder for any burned contact points. Moisture can damage the metal conductors inside the holder. If the holder is damaged, it should be replaced before installing a new bulb.
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Check all wiring for any signs of loose connections or burned wires. The ballast can overheat and melt low-temperature feed voltage wires. Use a volt meter and confirm that the correct voltage is being fed to the light fixture. Confirm the operation of the photocell if one is being used on the fixture. Wrap the photocell so no light enters into the receiver. Allow 5 to 10 minutes for the switch to activate. Test the overload relay or internal circuit breaker for continuity. Use the volt meter or an ohm meter to confirm that the safety switch is conducting power through the contacts. These switches are a one-time-use device and generally cannot be reset.
Ballast and Capacitor
Test the input voltage and output voltage of the ballast transformer. Check the manufacturer's specifications for wiring diagrams and voltages. Test the capacitor for proper storage capacity. Typically if the capacitor is not physically damaged or leaking oil, it is in good shape. If the windings show any sign of burning, replace the ballast. If all of the above checks are okay, then it is likely the ballast is damaged. Before closing the fixture, check all the seals. Moisture entering the fixture will damage the ballast. Steam can be generated by the excessive heat of normal operation. The steam can ruin the internal insulation of the ballast windings.