Here in the UK, at my local Tesco supermarket I saw some GLS bulbs which has a glass envelope that were slightly smaller than usual.
What's the idea behind this?
Wouldn't a 100W filament make a smaller bulb glass envelope get hotter than the larger standard envelope.
And therefore wouldn't this make the life shorter?
I don't know. Philips have started making theirs smaller. These smaller GLS lamps won't fit into a number of fittings my parents have because the neck is too short.
I wonder if GLS lamp sizes are covered by a British or EU statndard?
There are loads of factors which affect lamp life.
No. You simply increase the filliment thermal conductivity to the outside, by various means - usually the problem is isolating it from the environment - making the filliment cooler is easy.
I don't know exactly what this will do to efficiency, it's horribly complex.
As "meow" said, it saves material, reduces shipping and storage costs and allows more lamps to be placed in a given area of shelf space.
Yes.
Yes - if the lamp is not properly processed. There is a test called the "slumper can test" used in the lamp industry to check for processing contamination. A closed metal can is placed over an operating incandescent lamp. This heats the glass to higher than normal operating temperature. If the lamp is not clean then the higher glass temperature will drive contaminants such as water vapor out of the glass bulb, the filament will crack the water into hydrogen and oxygen and the oxygen will combine with the tungsten, causing the lamp to have shorter than normal life.
Does this mean that when I smear the bulb of my bedside light with aromatic oil such as bergamot (to make the smell diffuse into the room) then I am *noticeably* shortening the life of the bulb?
I'm not worried about a 3% or 4% reduction in life
But a shorter life by 15% or 20% is another thing.
No, not unless the glass bulb cracks (fractures). Vic, I believe, was talking about a chemical process -- like cracking petroleum to make oil and gasoline.
It's commonly believed, but not true, that a hotter bulb means shorter lamp life. As Vic said, if the lamp is made properly there's no relationship.
Lamp manufacturers have been moving toward smaller bulbs for some years for the reasons that others have mentioned. Once, all NA 100 watt lamps were "A-21" or 21/8 inches in diameter. Now, they are A-19 and some are smaller. There is a risk, of course, that higher bulb temperatures will increae the incidence of fire in portable lamps with flammable shades or if someone puts a high-wattage lamp into a socket intended for a lower-wattage lamp.
Terry McGowan
No. I was talking about contamination INSIDE the bulb. Your oil is on the outside. The glass keeps air out so it will obviously keep oil out :-) Now, if you completely cover the lamp with a thick enough layer of oil or any other material so that an insulating layer is formed AND the lamp was not properly processed so that it has residual contamination, then - perhaps.
Let me clarify my own statement.
The lamp life will be shorter only if there is contamination such as oxygen or compounds of oxygen such as water vapor on the inside glass wall or buried in the glass wall very close to the inside surface. When the bulb temperature is increased THIS contamination can be released into the bulb environment and oxidize the filament.
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