posted on Oct, 23 2005 @ 05:46 AM
Originally posted by shaunybaby
they could make edison's bulbs last a lifetime, but that wouldn't be right in the whole grand scheme of consumerism. also if they made a lightbulb
that lasted forever people would just leave their lights on all the time, this is why they make bulbs that blow, so people don't leave them on. even
though the onli time a bulb blows is when u switch it on/off because of the sudden flow of electricity through there, so actually if you don't want
your bulbs to blow leave them on all the time...
Wrong! By that load of erroneous info, I take you never have seen a lamp that is left on 24/7 burn out or know that turning it off/on cost less than
leaving it on.
How light bulbs burn out
Due to the high temperature that a tungsten filament is operated at, some of the tungsten evaporates during use. Furthermore, since no light bulb is
perfect, the filament does not evaporate evenly. Some spots will suffer greater evaporation and become thinner than the rest of the filament.
These thin spots cause problems. Their electrical resistance is greater than that of average parts of the filament. Since the current is equal in all
parts of the filament, more heat is generated where the filament is thinner. The thin parts also have less surface area to radiate heat away with.
This "double whammy" causes the thin spots to have a higher temperature. Now that the thin spots are hotter, they evaporate more quickly.
It becomes apparant that as soon as a part of the filament becomes significantly thinner than the rest of it, this situation compounds itself at
increasing speed until a thin part of the filament either melts or becomes weak and breaks.
Why making bulbs last longer often does not pay
You may have heard that the life expectancy of a light bulb is roughly inversely proportional to the 12th or 13th power of the applied voltage. And
that power consumption is roughly proportional to voltage to the 1.4 to 1.55 power, and that light output is roughly proportional to the 3.1 to 3.4
power of applied voltage. This would make the luminous efficiency roughly proportional to applied voltage to the 1.55 to 2nd power of applied
Now, if a slight reduction in applied voltage results in a slight to moderate loss of efficiency and a major increase in lifetime, how could this cost
The answer is in the fact that the electricity consumed by a typical household bulb during its life usually costs many times more than the bulb
Bulbs are so cheap compared to the electricity consumed by them during their lifetime that it pays to make them more efficient by having the
filaments run hot enough to burn out after only several hundred to about a thousand hours or so.
Do the math. LEDs consume far less wattage and last 50x longer.
There's money in making a light bulb last longer
The Great Internet Light Bulb Book, Part I
[edit on 23-10-2005 by Regenmacher]