I have a 20W (12V) desk lamp and a 25W (500 lm) bulb, type = G4/halogen.

I know putting a 75W bulb in a 60W socket can damage it or cause it to break.

In my situation there is only 5W difference.

  1. Would the extra 5W damage the lamp?
  2. Is it very dangerous?
  3. What could happen if I put the 25W bulb in?

I can't find a suitable answer on google so I thought I better be safe and ask stack exchange.


Here is a picture of the lamp if it helps:

enter image description here

  • 2
    \$\begingroup\$ It all about the ability to dissipate the heat. \$\endgroup\$
    – Aaron
    Aug 13 '20 at 18:26
  • 6
    \$\begingroup\$ If it could safely work at 25 W then it would be rated at 25 W. Think melting, catching fire, that sort of stuff. \$\endgroup\$ Aug 13 '20 at 18:43
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    \$\begingroup\$ @YoloGamer You need to follow the rating of the whole luminaire, not just the socket. \$\endgroup\$ Aug 13 '20 at 19:07
  • 5
    \$\begingroup\$ >>> "I know putting a 75w bulb in a 60w socket can damage it or cause it to break. In my situation there is only 5w difference." 75W in a 60W socket is 25% over-power rating. 25W in a 20W socket is the same --- 25% over. It's not absolute values that matter. If you put a 5W bulb in a 1W socket, that's only 4W over so it's OK?? Probably not \$\endgroup\$
    – Kyle B
    Aug 13 '20 at 19:23
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    \$\begingroup\$ @YoloGamer It could be dangerous just because of the power supply: 20 A of current flowing if the arms are shorted could weld something to them. \$\endgroup\$ Aug 13 '20 at 19:31

75 W om a 60W socket is 25% oversized

25W in a 20W socket is 25% oversized. so just as bad.

There's a good chance that something will break, and it might be the transformer in the base of that lamp, that part is most unlikely to have 25% excess capacity.


It may void your insurance cover. Or not.

I'd expect it to work well enough.
It may not.

A 5W LED lamp may produce 500 lumen (100 l/W)
A 6W one should. A 7W one almost certainly will./

I'd look at the illumination patterns of LED and Halogen bulbs.
The Halogen radiates upwards and downwards, with the upwards light reflected downwards.
Depending on design an LED bulb may have all light radiated in one direction - and the radiation angle may in any case be smaller than for a Halogen lamp.
Comparing actual results may prove useful.

A Halogen lamp will reduce in output over hundreds to a few thousand hours.
A reputable source LED lamp should have close top constant apparent output for 50,000+ hours.

The human eye/brain does not readily distinguish differences of illumination of perhaps 50%. All else being equal - if you have a say 500 lumen and 350 lumen lamp, if each is viewed independently, almost nobody could tell which was which.


In most cases lamps of that type have the 12V supply voltage present on the two uninsulated arms. This is a potential fire hazard even when limited energy power supplies are used. If the power supply is capable of supplying current well in excess of the lamp requirement the fire risk will be higher. This may invalidate your insurance cover, regardless of bulb wattage. A fuse (or better) is recommended.


I have so far been able to find a non-paywalled version of this paper, which describes the hazards due to low voltage low energy sources.

Vicars, Richard. Small, James. Munson, Terry. Parrish, Christopher.
Low Voltage: The Incompetent Ignition Source Dispelling the Myth. (2010).


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