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 Will Nicholes

Compact Fluorescent Light Bulbs (CFLs) vs Illuminated Light Switches

The Problem

Recently I discovered an interesting fact about illuminated (lighted) light switches: they don’t work very well with the new Compact Fluorescent (aka CFL) light bulbs.

There were a handful of light switches in my house that were hard to find in the dark, so I decided to replace them with illuminated switches. Once they were installed, however, the light bulbs they controlled would dimly flicker, even when the switch was “off.”

At first I assumed the light switch must be defective: since the light was flickering, that must mean the switch is allowing current to reach it, even though it’s in the “off” position. At that point I remembered something interesting about illuminated switches that I had forgotten: by design they’re always passing current through, whether they’re on or off.

This may seem odd, but it’s logical when you consider that in order for the switch to light up, it needs a circuit to pass through it.

Here’s an illustration of how a normal (non-illuminated) light switch works:

Normal light switch - off position

The black line with the yellow border represents the “hot” line, which feeds into the light switch. When the switch is “off”, the current stops there, and the black wire leading to the light fixture is not connected to the current.

Normal light switch - on position

When the light switch is on, then the current continues through the switch to the light fixture (the current is represented by the yellow border), through the light bulb (lighting it) and through the white (“neutral”) wire leading back to the circuit breaker.

A lighted (illuminated) switch behaves the same way when it is in the “on” position:

Illuminated light switch - on position

However, when it’s in the “off” position, the illuminated switch does something that may seem odd: instead of cutting the current to the light fixture, it simply reduces the current, so that its internal light (typically an LED or, in the case of older models, a neon bulb) can use the current passed through:

Illuminated light switch - off position

Without this current passing through, the illuminated switch would not be able to illuminate.

Since the current to the light fixture is significantly reduced when the switch is “off,” a normal incandescent bulb will not light. However, there is current passing through the bulb. To prove this, you can unscrew the bulb and see whether the illuminated switch stays illuminated. If it’s wired as shown above (and most are), removing the light bulb will cause the switch itself to go dark.

Even though there’s not enough current passing through to light an incandescent bulb, many compact fluorescent lights are sensitive enough to small amounts of current that they will flicker on and off, or even maintain a constant dim glow, when the lighted switch is “off.”

The above illustrations show the wiring for regular “on/off” illuminated switches, but the same principles apply to three-way switches and four-way switches. In fact, if more than one illuminated switch is attached to the light fixture, the problem may be even worse.

What to do

In most cases, you simply have to choose which is more important to you: the compact fluorescent, or the illuminated switch. In my case, I decided to replace the flickering CFL with a regular (incandescent) bulb.

Another option is to keep the CFL(s), but replace the illuminated switch(es) with regular switches. This is the more energy-efficient option, and there are glow-in-the-dark faceplates you can buy which will absorb light during the daytime and release it in the dark. These faceplates work best when lots of light is normally available to them which they can absorb.

A third option is to install a switch with a pilot light. A pilot light works on a different principle from an illuminated switch, and the current to the light fixture is always either entirely on or entirely off.

Switch with pilot light

However, this option is only available to you if both the hot (black) and neutral (white) wires are accessible in the switch box. Many light switches only contain the hot wire, so a pilot light switch is not always feasible. Pictured above and below are two pilot light switches I installed in my house in the summer of 2006.

Switch with pilot light

If in doubt about what type of switches to install, consult an electrician.

 

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