"it is hard to understand how voltage could be too high to some fixtures. The voltage coming into the house is set by the power company, and distributed throughout the residence. I can see it going down, but not up?"

The supply voltage is not individually regulated for each house or service, or even for each neighborhood. In most cases the closest point of adjustment is at the substation, which sets the voltage for a whole area. And it's not an instant-response, fine-adjustment thing, either. Your service voltage probably goes up and down several percent in the course of a day.

Nearly all residential electric services in the USA are three-wire 120/240 volt grounded-neutral, from by a local transformer that feeds several homes.

This means you can get 120 volts for most uses by connecting between one of the "hot" wires and the neutral, or 240 volts for special purposes like the stove or clothes dryer by connecting between the two "hot" wires. This system goes back to Edison and has lots of advantages.

BUT, if the 120 volt loads are not somewhat-evenly balanced, or the neutral connection has significant resistance, the voltage on one "hot" wire can be higher than on the other.

"Clearly some fixtures get switched on and off more than others. But if CFL's cannot handle this as well as incandescants, then that should be a factor in their description of "suitability for use", and in predicted lifespan vs continual use."

All flourescents' life is reduced by frequent on-off cycling. The same is true to a lesser extent for incandescents (how many times has an incandescent failed with a flash when you turned it on?).

CFLs are *not* suitable for all applications. Frequent on-off cycling is one; extreme low and/or high temperature is another. That doesn't mean they are worthless, just that they're not a cure-all.

"light fixtures, usually ceiling fixtures, that are a pair of bulbs covered by a globe or hemisphere of glass. If this means that there is too much contained heat for CFL's to last, compared to incandescents in these same fixture, then that also should be a factor in designating suitability for use as not much can be done other than replacing the entire fixture."

Most fixtures have a warning label about maximum wattage. That label is about heat. Ignoring it can be the source of many problems.

Replacing a fixture is not a big deal. Too often, lighting fixtures are designed for how they look rather than for their effectiveness and efficiency.

"My impression is that CFL's, compared to incandescants, are just not as reliable overall."

The problem is that the technology is still new and there are enormous variations in quality and suitability for various applications. Incandescents went through the same thing, over 100 years ago.

One thing I do, whenever replacing a bulb of any type, is to write the installation date on the base (not the glass). That gives me real-life information.

Another test is to mix an incandescent and a CFL in a multilamp fixture or multiple fixtures on the same switch, and see which really lasts longer.

What we *really* need here in the USA is more-rigorous testing, quality control, and information-labeling of CFLs. We shouldn't have to be running our own private experiments as to how well a particular brand works in the cold, how many on-off cycles to expect, what the real-world MTBF is, etc.

The LED bulbs I've looked at are more compact then similar output CFLs. So if you have a fixture can't accept a CFL, the LED might work.

The LEDs are also more directional, which might be a plus or negative depending on the application. They would make a great reading light, for instance, but aren't as good for diffuse room lighting.

The numbers the author calculated comparing the lifetime cost are a little off. Most 10 W CFL are cheaper than the $6.95 he quotes and most of us pay less for electricity. So the lifetime cost of the LED would look higher compared to the CFL.

Of course, if they get the efficiency of the LEDs closer to their theoretical limits, this will all change.

In responses to my comments about short life spans for CFL's vs incandescents, three issues were raised:

1) voltage

2) on/off cycles

3) heat

Considering voltage, it is hard to understand how voltage could be too high to some fixtures. The voltage coming into the house is set by the power company, and distributed throughout the residence. I can see it going down, but not up?

On/off cycles: Clearly some fixtures get switched on and off more than others. But if CFL's cannot handle this as well as incandescants, then that should be a factor in their description of "suitability for use", and in predicted lifespan vs continual use. (My experience is that CFL's fail in this situation).

Heat: We all have, or have seen, light fixtures, usually ceiling fixtures, that are a pair of bulbs covered by a globe or hemisphere of glass. If this means that there is too much contained heat for CFL's to last, compared to incandescents in these same fixture, then that also should be a factor in designating suitability for use as not much can be done other than replacing the entire fixture.

My impression is that CFL's, compared to incandescants, are just not as reliable overall. I was willing for a couple of years to spend the extra money for CFL's but that just does not seem plausible any longer, except in those fixtures where the lamp is either on most of the time, or only now and then (but mostly off). Regular switched use gets the old fashioned bulb from me.

"The light fixture that wears out quickly is in a small box-like space covered by a thick piece of glass, so it must get hot in there- no wonder the bulb burns out so often. I will try switching the glass."

You may need to do more than that, particularly with a high-wattage bulb. What matters is how hot the bulb gets.

"I have a dimmer switch hooked up to my bedside lamp, which means that the bulb receives lower voltage, and thus lasts longer."

A CFL that isn't meant to be on a dimmer will have a short and dramatic life when used with one.

Running an incandescent on even slightly lower than design voltage will dramatically increase its life - and dramatically reduce its efficiency. For example, if you run an incadescent at 80% of its design voltage, it will last 20 times its normal-voltage lifetime. But the efficiency (amount of light per watt) will be about half of its normal-voltage value.

"Now if only I knew why the lightbuln in my kitchen light seems to burn out so often- it's in a well-ventilated location and not on a dimmer, though we do turn it on and off five or six times a day. Is that considered "frequent"?"

No.

However the *fixture* may not be well ventilated. What matters is how hot the bulb gets.

"Should I use an incandescent? The electrical system of the (rental) house is definitely a bit shady, so I wouldn't be surprised if it's not receiving consistent voltage."

Consider replacing the fixture and/or writing date-of-installation on the bulbs. Relying on memory can be tricky.

Ceiling lights and those near doors are particularly susceptible to failure from vibration, due to door-slamming and "heavy walkers" above. Consider rugged-service bulbs for such applications (they do exist, but watch out for left-hand threads).