Why Do Bathroom Lights Flicker on and Off? Understanding the Physics Behind Flickering Incandescent and Fluorescent Bulbs

Have you ever experienced the frustration of your bathroom lights flickering or even stopping to work temporarily before resuming their normal operation? Understanding the science behind this phenomenon can help you identify the probable causes and work towards a solution.

Understanding the Power Circuit Dynamics

In most power circuits, there is a mix of resistive and inductive loads. Resistive loads include heating elements like toaster and incandescent light bulbs, while inductive loads encompass anything with a motor - vacuum cleaners, microwaves, pumps, and electric toothbrushes.

Faraday's Law of Induction

Faraday's law of induction states that the back EMF voltage induced in an inductive load is proportional to the rate of change in current. When the load is steady, the rate of change of current is zero, hence no induced voltage. However, when the load is switched off, the current drops from a steady state current down to zero, creating a high rate of change in current.

The induced voltage, or back EMF, in the inductive load is the product of the inductance (measured in Henrys) and the rate of change of current. With a high rate of change of current, specifically from a steady state value down to zero, the back EMF can be high enough to cause an incandescent light to flicker. This is a phenomenon that can be observed by plugging a vacuum cleaner into the same outlet as a lamp. When the vacuum cleaner is turned on, the brightness of the lamp increases for a split second, and when the vacuum cleaner is turned off, the lamp flickers again.

Common Causes and Solutions

There are several common causes for flickering lights, including a failing switch, a loose bulb, or other connections that are getting fidgety.

Checking the Switch

First, it's worth checking the switch. It might be about to fail, or there might be a loose connection. Simply wiggle the switch and see if you can make the flickering happen again or if the handle feels loose or moves side to side.

Historical Case: Switch and Fluorescent Bulbs

Back when I had cheap rocker switches for my lights, I used to experience problems specifically with fluorescent lights. The issue was resolved after I replaced the old switch and cleaned the terminals of the fluorescent tubes. The switch was around 30 years old at the time.

Dirty Switch Contact

Another probable cause for flickering lights could be a dirty switch contact. This is due to the slight arcing that occurs every time the switch is used. Sometimes, this issue only arises once out of numerous switch actions and then clears again.

Conclusion

Bathroom lights flickering or briefly stopping can be a nuisance, but understanding the physics behind these occurrences can help you pinpoint the probable causes and take appropriate measures. Whether it’s a failing switch, a loose bulb, or a dirty contact, troubleshooting these issues can restore your lights to healthy function and turn down the frustration level.