Lightbulb Differences: Investigating Unusual Outcomes

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SUMMARY

The discussion centers on a lamp malfunction after replacing a lightbulb rated at "240V; 500W" with a fixture marked "MAX: 230V; 300W". The user, fawk3s, experienced the new bulb not lighting after initial use, leading to an investigation into potential causes. Key insights include the possibility of lamp socket failure due to oxidation or overheating, as well as the behavior of tungsten lamps drawing higher current upon startup. The discussion highlights the importance of matching bulb specifications with fixture ratings to prevent damage.

PREREQUISITES
  • Understanding of electrical ratings (voltage and wattage)
  • Basic knowledge of lamp and bulb specifications
  • Familiarity with electrical formulas, particularly N=UI (Power = Voltage x Current)
  • Awareness of common lamp fixture issues, such as thermal fuses and contact spring failures
NEXT STEPS
  • Research the implications of using bulbs with higher voltage and wattage ratings than fixture specifications
  • Learn about the behavior of tungsten lamps during startup and their current draw characteristics
  • Investigate common lamp socket failures and maintenance practices
  • Explore the function and types of thermal fuses in light fixtures
USEFUL FOR

Electricians, DIY enthusiasts, and anyone troubleshooting lamp and lightbulb compatibility issues will benefit from this discussion.

fawk3s
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I recently ran into the situation where one of my lamps lightbulb burned out. So I changed the bulb. I left home for a second and when I came back, the bulb wasnt burning anymore. So I started to investigate it.
Turns out the new bulb didnt burn out. Everything seems to be ok with it, but then I noticed the sign on the bulb which said "240V; 500W". So I immediately checked the lamps aswell. That one said "MAX: 230V; 300W".
Calculating by the formula N=UI, we get that the maximum current for the lamp/the old bulb could be approximately 1,3A. For the new bulb it could be about 2,1A.

I haven't bought a new bulb for the lamp yet, but I am interested what actually happened there.
What happened that caused the bulb not to burn anymore, even though it burned at first?
Did the bulb "demand" too much out of the lamp and damaged it somehow?
Or did something happen to the bulb?

I haven't tried the lamp with a new bulb, and I have examined the bulb carefully. It seems to be fine looking outside.

Thanks in advance,
fawk3s
 
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The lamp socket could have failed from oxidation or overheating. Contact springs will relax when overheated. Some light fixtures have a "thermal fuse". Different types will temporarily or permanently open if the fixture overheats.

Failure of the fixture was probably not the current directly. Tungsten lamps will draw many times their operating current when voltage is first applied.
 

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