Half a croissant, on a plate, with a sign in front of it saying '50c'
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Double glazed lightbulb

Fit the best. Or fit these instead
  [vote for,

Heated filament lightbulbs are old and rubbish.
They waste a lot of energy, giving out only one fifth of the light that fluorescent lightbulbs do per Watt.

Nevertheless, perhaps they could be made more efficient by insulating them more effectively, so less heat would be lost. This could probably be done fairly easily and at low cost by adding a second, inner, glass bubble.

Loris, Jan 12 2004

Lamp with IR reflectivity http://164.195.100....620&RS=PN/6,281,620
Increasing eff. by 50% [ldischler, Oct 04 2004, last modified Oct 05 2004]


       I'm pretty sure that the heat generated is a by product of the light, conserving the heat wouldn't change the energy put into generating the light. In fact it may be counterproductive by increasing the temperature of the filament and causing the resistance to rise. Or causing it to fail altogether.
kracker, Jan 12 2004

       so [kracker] instead of double glazing are you advocating mini fridges around filaments to keep them cold ?
neilp, Jan 12 2004

       They glow because the filiment's hot. If you heat it up it will glow brighter but won't last as long. Cool it down and it will last longer but won't shine as bright.
Worldgineer, Jan 12 2004

       Double-glazing won't prevent IR from escaping, which is the main problem. There are reflective coatings that work, though.
ldischler, Jan 12 2004

       To be honest, I am not entirely sure how the wattage of a lightbulb is regulated. I don't think 100W bulbs last a shorter time than 60W, or even 40W ones (but I reserve the right to be wrong).
However, I do agree that the light is produced solely as a result of the high temperature of the filament.
I would like to think that if insulation worked you'd just get a brighter bulb for a lower wattage. The working temperature of the filament would be the same as that of an equivalent (but higher wattage) uninsulated bulb, so it wouldn't fail quicker.

       I am tempted to speculate that I may get less fish for "mirrored lightbulbs", ldischler. You may well be right that infrared is the major energy loss, in which case an infra-red reflective coating would be beneficial (and is probably already used).
Loris, Jan 12 2004

       The wattage is more-or-less inversely proportional to the resistance of the filament. So a 60W bulb has 2/3 the resistance of a 40W bulb. Lower resistance means more current flows, and more power is used.   

       Does anyone know why clear bulbs are so big? There's a lot of space around the filament.
sandfly, Jan 12 2004

       //Does anyone know why clear bulbs are so big//
I expect it's to do with the fact the gubbins in the metal part takes up a certain diameter and for the formation of a sphere equidistant from the filament this diameter depicts the size of the sphere.
silverstormer, Jan 12 2004

       Purely decorational. I've seen clear bulbs that range in size from mini-candelabra way up to giant globes, and in many different shapes as well.
Freefall, Jan 12 2004

       It may also be to keep the glass cooler?
my-nep, Jan 13 2004

       MIT's been working on this in recent years, using a coated filament instead of double glazing, and they think incandescent bulbs may soon be able to compete with LEDs on efficiency.
notexactly, Mar 30 2017

       From a English - Welsh - Scottish - Northern Ireland (please delete as the UK fragments) perspective, incandescent bulbs are kind of handy, as it's so frikkin' cold all year round. That they produce light as well is merely a handy by-product.
not_morrison_rm, Mar 30 2017


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