The snap answer is “because no one ever made a flat lightbulb“, but Wired UK now puts the lie to that one: someone displayed a flat lightbulb concept at a design show back in 2008, apparently, though it seems never to have made it to production.
The second (and more considered) answer would probably be “because when they were first being made, limited technology for glass manufacture meant that globular capsules were easier and cheaper to produce, and by the time the technology had improved the shape of a lightbulb was an established given that no one thought to alter“. (I’m not certain about the limitations of early manufacture, but it’s a self-educated guess; anyone who can enlighten me further?)
The paranoid answer might be “their frangibility appeals to the sort of corporate mindset that came up with the concept of planned obsolescence” – in other words, lightbulb makers make lightbulbs that are easy to break because they can then sell more lightbulbs. Pretty sure there’s a logical flaw in there somewhere, though…
But anyway, this tangential waffling is the result of that lightbulb story making me wonder how many other household objects are the shape they are, just because they’ve always been made that way. And from there, it’s a short step to thinking similar thoughts about intellectual and cultural institutions, political theories and so forth…
… yeah, so I’m having one of those Fridays where my mind wanders a lot. Lucky you, eh? 🙂
It’s always good to question The Way Things Have Always Been Done, but in this case, the answers I get tell me that it really DOES make the most sense.
Incandescent bulbs were originally round for a lot of reasons:
1) It was easier to blow a simple shape in the large quantities required.
2) A spherical or near-spherical shape is the most efficient for a pressure-containing vessel, no matter which side the low pressure is on.
3) A spherical envelope allows the most uniform distribution of light from the filament, which is effectively a point-source.
Even after technological advances could have obviated point 1), the other two points still hold.
After a few decades, point 4) emerged: back-compatibility. Anyone who’s tried to cram a compact fluorescent into a ceiling fixture whose globe isn’t QUITE big enough will appreciate a technology with replaceable components that were compatible for OVER A CENTURY.
The now-familiar spiral shape of a CF “bulb” is expressly to maintain that backwards compatibility, and to create a more uniform light distribution. The original CFs were closely-packed straight cylinders; only the lowest-powered versions would fit in any kind of enclosed lamp, and the light distribution was … odd. Even the spiral bulbs have a massive shadow at the bottom, thanks to the big plastic circuitry housing. If they could make CF bulbs that were genuinely spherical (rather than a spherical cover over a glass spiral), they would.
In my experience, the typical mode of failure for an incandescent bulb isn’t breakage, it’s filament burnout. Changing the shape or the thickness of the envelope is over-engineering.
As someone pointed out in a comment on the link, that flat bulb design didn’t emerge until the incandescent bulb was obsolete. By 2008, there was already talk about incandescents being phased out entirely by legal mandate.
3 above seems obvious to me 🙂
“…how many other household objects are the shape they are, just because they’ve always been made that way. And from there, it’s a short step to thinking similar thoughts about intellectual and cultural institutions, political theories and so forth.”
The tempting element of this mental path is the desire to think of oneself as the Brilliant Young Mind with the Insight to Throw Off Decades of Stultifying Tradition and Think For Oneself!
In practice, I find that entropy has a better track record of eliminating the inefficient and the counterproductive than one might expect, in just about every field of endeavour or practice. There usually do turn out to be good reasons why things are the way they are, and if something’s been around for a while, it’s usually because it’s working adequately.
(Which is not to say that we won’t always need skeptics and why-notters and what-iffers, or that they aren’t sometimes right. Just that they’re not always right, and they’re not even right as often as they’d like to think they are.)