How To Safely And Properly Change A Metal-Halide Bulb In A Light Tower

Light towers are indispensable to oilfield rental operations because they permit the time-sensitive work of mineral extraction to carry on around the clock. However, like any piece of lighting equipment, from a flashlight to a stadium floodlight and everything in between, light tower bulbs will eventually fail and require replacement. Replacement isn't complicated, but it isn't as casual as changing a table lamp bulb in your home; that's why you should understand the correct procedure for changing these high-wattage, metal-halide bulbs. Below is a guide to the tools and materials needed as well as a step-by-step procedure for removal of the old bulb and installation of the new one:

Tools and equipment needed

  • Screwdriver or nut driver in the appropriate size

  • Metal-halide bulb

  • Cotton gloves

  • Adjustable wrench

  • Isopropyl alcohol in 91% concentration or higher

  • Microfiber towel

  • Liquid glass cleaner

  • Safety glasses

  • Infrared thermometer

Step-by-step procedure

1. Make your personal safety a priority - even though changing a bulb may seem mundane, it can be hazardous if you don't approach the task with caution. The electrical generators used in light towers can produce hundreds of volts with large numbers of amps; accidental contact with a power terminal can have fatal consequences. In addition, metal halide bulbs generate thousands of degrees of heat and can cause serious burns. These same bulbs can also suddenly and violently explode, sending glass fragments flying. Don't allow yourself to be injured or killed, so be sure that working safely is always paramount when changing bulbs.

2. Turn off the electrical system and disconnect power cables - the first task when changing a bulb is to turn off and disable the electrical system in the light tower. While removing generator start/run keys is important, keep in mind that someone may have a duplicate key and use it to start the system. That's why you should also disconnect the battery cable leading from the generator's electric starter; this will prevent accidental startups from occurring.

3. Make the light bulb accessible - in most light towers, the bulbs are hoisted into position on a tower that can be readily raised and lowered. Never attempt to replace a bulb on a raised tower unless you have no other option; take the time to lower the bulb fixture to the ground where it can be safely handled.

4. Allow the bulb to cool before handling - as mentioned earlier, the metal halide bulbs used in light towers are both hot and susceptible to breaking. Permit the bulbs to cool completely before handling them; even a broken bulb can retain heat for a while. Use an infrared thermometer to measure the bulb's temperature if you have doubts about its ability to be handled.

5. Remove the light fixture cover - most light fixtures use a tempered glass cover that protects the light from rain, snow and other outdoor elements; this cover will need to be removed before changing the bulb. Put on your safety glasses, and remove the screws securing the cover to the bulb housing. Carefully pull the cover away from the housing, being careful not to disrupt or tear the cover gasket, and set it aside in a safe location.

6. Remove the bulb - put on your work gloves and grasp the bulb by wrapping your fingers around the mid-portion; do not pinch the bulb or you may cause it to shatter. Turn the bulb counterclockwise to loosen it and remove it from the fixture once it is free of the socket. You may also need to remove the tip of the bulb from a restraint, so be aware of that possibility if your particular tower model possesses that feature.

7. Clean the inside of the housing and cover- once the bulb is removed, take a moment to wipe down the inside of the housing with a microfiber towel; insect carcasses, dust and other debris can shorten the lifespan of the new bulb or even obscure the light output in some circumstances. In addition, use glass cleaner and a towel to thoroughly clean the glass cover. Be sure to inspect the gasket that helps keep out debris and adjust it into its appropriate position if it has been dislodged.

8. Install the new bulb - when the housing is clean, you can install the new bulb. Verify before opening the new bulb container that the bulb's wattage matches the specifications of the lighting unit; a mismatch could cause the bulb to burst upon use. Should the bulb contain fingerprints, a cause of premature failure, pour isopropyl alcohol over the glass and use a paper towel to remove the fingerprints. Allow the bulb to air dry before insertion.

Once the bulb is ready to install, put on gloves and insert the bulb into its socket and slowly turn it clockwise; if the bulb binds, stop and back it out a turn or two, then attempt to insert it again. Continue turning the bulb until it won't easily move, then stop turning to prevent damaging the bulb or socket. Secure the bulb in its restraint, if the housing possesses such a feature.

9. Replace the cover - place the cover onto the housing, being careful not to dislodge the gasket. Insert the screws and tighten them until the cover is secured.