The Naked Scientists

The Naked Scientists Forum

Author Topic: What causes a light bulb to burn out?  (Read 21740 times)

abbey

  • Guest
What causes a light bulb to burn out?
« on: 14/12/2010 17:30:02 »
abbey  asked the Naked Scientists:
   
What causes a light bulb to burn out or "blow"?

What do you think?
« Last Edit: 14/12/2010 17:30:02 by _system »


 

cat_with_no_eyes

  • Guest
What causes a light bulb to burn out?
« Reply #1 on: 14/12/2010 17:59:26 »
If you compute the average life of your bulbs and discover it's clearly less than the manufacturer's rated life, then you may have:

    * You may have over-voltage in your house.  Occasionally this causes more serious problems.  You can get a cheap multimeter at Radio Shack. If the voltage is 125V or higher, talk to the power company about it.  7 or 8 extra volts on a 120V line will cut the bulb life expectancy in half.  If it's a slight over-voltage, you can buy special 125V or 130V bulbs, though sometimes they're hard to find.
    * Too high a wattage bulb in too small an enclosed fixture (such as a globe), the heat can't get out--the bulb burns too hot, leading to short bulb life.
    * Recessed lighting fixtures often get covered by attic insulation. This blocks the intended ventilation method--heat can build up around the bulb, causing short bulb life.
    * A vibration problem. Such as, bulbs under a heavily used stairway, on or near an out of balance bathroom or ceiling fan, or near a door that gets slammed, or kids upstairs jumping, etc. You can buy special shock resistant, also called "rough service" bulbs, for this situation, or try one of the new compact screw-in fluorescent bulbs.
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
What causes a light bulb to burn out?
« Reply #2 on: 14/12/2010 20:37:19 »
They also fail when they get old  :D

Assuming we are talking about old fangled filament bulbs, the filament eventually wears out.

The filament tends to have variations in temperature along its length. At the hotest places along its length the filament evaporates more quickly. This evaporation further increases the temperature at that spot, and the rate of evaporation accelerates until the filament completely evaporates at that position on the filament.
 

Offline maffsolo

  • Sr. Member
  • ****
  • Posts: 280
    • View Profile
What causes a light bulb to burn out?
« Reply #3 on: 15/12/2010 01:19:08 »
I think I heard that mishandling a filament lamp can also have an affect on its lifespan.
Besides slamming it against the floor, the natural oils from a human touch can cause a blemish on the glass causing it to have a hotspot when heating up, fracturing the glass making the vacuum escape, oxidizing the filament, making the lamp malfunction.
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
What causes a light bulb to burn out?
« Reply #4 on: 15/12/2010 01:52:56 »
I think I heard that mishandling a filament lamp can also have an affect on its lifespan.
Besides slamming it against the floor, the natural oils from a human touch can cause a blemish on the glass causing it to have a hotspot when heating up, fracturing the glass making the vacuum escape, oxidizing the filament, making the lamp malfunction.

I believe that is true with halogen cycle bulbs. The quartz envelope gets hot enough to alter the structure of the quartz where there is oil on the surface.
 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
What causes a light bulb to burn out?
« Reply #5 on: 15/12/2010 13:07:18 »
You may have over-voltage in your house.  Occasionally this causes more serious problems.  If the voltage is 125V or higher, talk to the power company about it.

If I'm getting *only* 125V in my house, I'd be pretty concerned!
We are meant to get 240V in the UK!
 

Offline keirastone

  • First timers
  • *
  • Posts: 2
    • View Profile
What causes a light bulb to burn out?
« Reply #6 on: 15/12/2010 13:51:32 »
well, i guess that the filament inside the bulb made it like a burn but it lite so fast that we can't see that it is burning but lighting, and this happens at the speed of light therefore when we on the bulb then it on the spot spread the lite in the room or house .
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
What causes a light bulb to burn out?
« Reply #7 on: 15/12/2010 18:20:05 »
You may have over-voltage in your house.  Occasionally this causes more serious problems.  If the voltage is 125V or higher, talk to the power company about it.

If I'm getting *only* 125V in my house, I'd be pretty concerned!
We are meant to get 240V in the UK!

It's my understanding that you are only supposed to get 230 Volts these days.
 

Offline peppercorn

  • Neilep Level Member
  • ******
  • Posts: 1466
    • View Profile
    • solar
What causes a light bulb to burn out?
« Reply #8 on: 15/12/2010 19:34:11 »
It's my understanding that you are only supposed to get 230 Volts these days.

Well, I'll be - So we are! Since the beginning of 2004 apparently!
In line with the EU standard, so it says 'ere.
Why wasn't I informed of this? :D
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
What causes a light bulb to burn out?
« Reply #9 on: 15/12/2010 22:43:02 »
It's my understanding that you are only supposed to get 230 Volts these days.

Well, I'll be - So we are! Since the beginning of 2004 apparently!
In line with the EU standard, so it says 'ere.
Why wasn't I informed of this? :D

You are probably still getting something closer to 240. The tolerance on the 230 standard is large enough to include 240  ;D

"The great thing about standards is that there are so many to choose from!"
 

Offline techmind

  • Hero Member
  • *****
  • Posts: 934
  • Un-obfuscated
    • View Profile
    • techmind.org
What causes a light bulb to burn out?
« Reply #10 on: 18/12/2010 22:44:07 »
The harmonisation of Europe's electricity voltage is a political fudge. Although officially we're all "230V", in practice we keep our 240V, continental Europe keeps their 220V ... but the tolerances are fudged so that we have 240V +6%/-10% and they have 220V +10%/-6% (which the last time I checked covers the same range).
In practice it is expected that the UK will nedeavour to supply 240V  +/-6% as it always has.

As others have pointed out, the lifetime of a bulb is highly dependent on the voltage (approximately following a 12th power of the voltage relative to nominal?) and for this reason the UK still has "240V" filament bulbs and the continent "220V" ones.
Compact-fluorescent bulbs have electronic inverters built in, and should tolerate a wider range of supply voltage.
 

The Naked Scientists Forum

What causes a light bulb to burn out?
« Reply #10 on: 18/12/2010 22:44:07 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length