CFL light bulb humming or Digital Clock running fast – household alert!

This story starts with us noticing that the digital clock in our bedroom was always getting ahead in time. It did not occur to us at first that the problem was not with the clock. After getting a fancier model we were surprised that the new clock was ticking faster as well. At this point we realized that this anomaly happens only when the light is turned on. We had replaced our lighting in the bedroom with CFL bulbs shortly before and it was on a dimmer switch. We had not noticed anything significant with the CFLs, except for a background humming.

From a layman’s point of view, the dimmer works by turning power on and off at a very high frequency. The CFL (Compact Fluorescent Light) humming occurs when the electronic ballast inside the bulb that regulates energy flow malfunctions due to the lack of consistent power because of the dimmer. The humming can also occur even when there is no dimmer, if the electronic ballast is faulty. This is a a fire hazard and replacing the bulbs is the only solution – bulbs compatible with dimmer switches are now available. The marking in the package clearly indicates compatibility with dimmer switches.

The reason for the digital clock running too fast can sound rather strange. Turns out that the AC powered digital clocks use the line frequency of the power line instead of a quartz crystal to calculate time. Any variation in line frequency, will affect the digital clock’s accuracy. The malfunctioning of the electronic ballast in the CFL causes variations in the line frequency. Couple of scenarios where AC digital clock accuracy could go awry are
  • It is used at a different line frequency than it is designed for – this can happen if you travel with an AC line clock and your destination country uses a different line frequency than your home country.
  • The AC digital clock is on an inverter circuit.

Another aspect of CFL’s that everyone needs to be aware of is the existence of 5mg mercury in the bulb. Practicing safe disposal is paramount!!

Last Updated: 01/2015.


1 comment :

Anonymous said...

Just to let you know: I thought GE sounded like a reliable brand to try for CFLs marked as dimmables for the first time: maybe I got some early manufacturing runs (late 2007) of their flood version bulbs, but I tried two on a Lutron slide dimmer. They both blew up (when I say "blew up", I mean it literally)and they were labeled as containing mercury, of course.

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