In om, hobbes wrote:
Hi,

I have a Lutron dimmer that dims a 100w (4 x 25w) light fixture in a
bathroom. I noticed that one of the 25w bulbs was out and that the
dimmer does not dim any more. My question is can a bulb burning out
cause a sufficiently high current transient / short to burn out a
dimmer?

I read in this news group that bulbs blowing can be a reason that a
dimmer fails. Is this true?

A bulb blowing, especially the usual burnout with a bright blue flash,
can take out the dimmer.

The bright blue flash is a "burnout arc", which can briefly draw
something like 100 amps or more for a few milliseconds. The dimmer may be
made as cheaply as possible, and could only "usually" as opposed to really
reliably survive the current surge of a burnout arc.

I have also heard of complaints of a few lightbulbs lacking fusible
links in their necks. Those are supposed to blow if a burnout arc draws a
really bad current surge. In extreme cases, I have heard of bulbs without
fusible links failing badly with the glass bulb popping off the base. My
guess is that the wires violently vaporize adjacent glue/cement due to an
extreme current surge drawn by a burnout arc.

Lightbulbs of "Big 3" brands (GE, Sylvania, Philips) probably have fewer
issues in this area. Store brand lightbulbs of "usual regular shape and
size" and 25, 40, 60, 75 or 100 watts and same hour life expectancy
figures and same lumen light output figures as "Big 3 brand" ones are "Big
3" ones with the only difference being the brand or lack thereof printed
on the top of the bulb.

Lowest prices I have seen for "standard" "Big 3" lightbulbs: At Lowes.

Another idea: Use compact fluorescents and do without the dimmer. Four
7-watt spirals will outshine four 25-watt incandescents, and a 25 watt
incandescent dimmed to the point of consuming 7 watts will produce about
1/4 or less the light of a 7 watt nightlight. If you never or hardly
ever need less light than that and dim only for energy conservation
purposes, go for compact fluorescents if you don't need dimming.

Now another idea: Compact fluorescents often do not do well in
bathrooms often used for short trips - unless they are cold cathode! And
cold cathode ones are dimmable. They are somewhat less efficient than the
usual hot cathode ones, but still a lot more efficient than incandescents.
Online lightbulb sellers sell ones up to 8 watts, which are about as
bright as 25 watt incandescents. They are rated to last 25,000 hours and
do not suffer extra wear from starting, and are even rated for
flashing/blinking duty. What mainly tends to go wrong with those is that
they fade as the phosphor gets worn out over the years, otherwise they
fail from breakage or the electronics blowing from an especially bad power
surge that blows electronic products.

Still another idea: If there is a need for dim light as well as bright
light, the most energy-efficient option is to have separate light sources
for those. (Though dimmable compact fluorescents are a close second and
quite convenient.) The dim-light source could be a nightlight having a
built-in switch and the traditionally incandescent bulb replaced by a 3
watt cold cathode compact fluorescent, such as the 3-watt N:Vision one
available at Home Depot. If you like less light than that, LED
nightlights do well there with usually around 1 watt of power consumption.

- Don Klipstein )