Your company has made green part of its mission. Last summer involved upgrades of all of the lighting. In most cases, this was a matter of replacing old fluorescent fixtures with new ones. The new ones provide more light with the same wattage, due to improved lamps, ballasts, shades, and lenses.

Recently, however, you've had complaints that the lights are too dim. Using a light meter, you took new readings against the baseline survey taken after each area was upgraded. Sure enough, there is less light. In some cases, the lumens are almost 25% less than the baseline readings.

How can you track down the cause(s)?

It's very unlikely the ballasts and lamps have deteriorated this much so soon. You could install new replacement ballasts and lamps on one branch circuit to verify this, but that's a lot of work and it won't identify or solve the cause(s).

Start with these seven steps:

  1. Check the lenses. The fixture design may let dust accumulate on the lens, lowering light output. If the lenses are that dirty this soon, contact the manufacturer for advice.
  2. Check the shades. If the lights have adjustable shades, louvers, or other light-controlling surfaces, maybe the original adjustments didn't hold.
  3. Do a power analysis. The new ballasts may interact with the power supply or other equipment in a detrimental way.
  4. Check for new loads. If people are now using personal space heaters, the loads may reduce voltage on lighting branch circuits.
  5. Check for bonding. If you have grounding (connected to earth; see Art. 100 definition) rather than bonding, you probably have circulating harmonics.
  6. Conduct insulation resistance tests on the wiring. Leaking insulation means fewer watts producing lumens.
  7. Conduct low ohms tests on the wiring. Using a low ohms meter set for the branch circuit voltage, look for high-resistance connections.