I had to replace the hall lightbulb today and there were two sets of lightbulbs available in the closet - a 60 watt bulb and a 100 watt bulb. I wasn’t sure which one needed to go in, so I looked at the dead bulb. It said 60 watts so I replaced it with another of the same type.
Now, for the question:
What would have happened if I put a 100 watt bulb in there? Would it even make a difference since the bulb’s capacity is greater than the electrical output?
What if I put a 60 watt bulb in a 100 watt socket?
It largely depends on the design, orientation and construction of the fixture. Most fixtures will specify a maximum wattage, for the simple reason that exceeding this can result in excessive heat buildup, which in turn can lead to things like electrical insulation failure. This, of course, can be bad. If you are unsure of a fixture’s maximum wattage rating, sticking with 60 or even 75 watts is almost always safe. All things being equal, recessed ceiling-mounted fixtures will tolerate higher wattages less well than an open table or floor fixture.
The two general things you have to watch for are the local heating, and the current through the circuit breaker that circuit is on. The 100W bulb is going to draw more current and give off more heat than the 60W bulb.
The circuit breaker is likely to have no problem with a 100W light bulb – but I can’t be sure without knowing everything on that circuit; they all add up to a total that needs to be a lower current than the circuit can handle. Nevertheless, I’d be surprised if the circuit breaker is an issue there. (If it is so close to capacity that the difference between 60W and 100W is an issue, you need to back down on other parts of the circuit.)
A more likely problem would be the heat. Some fixtures are designed to handle the heat (in terms of a heat sink, the type of wiring), and some aren’t. Look at the fixture, with the cover (if any) off – does it have any markings that tell you a maximum wattage for the fixture? Heed them.
Otherwise, I couldn’t tell you. It’s always safe to put a lower wattage bulb in a fixture that can handle more – it just won’t be as bright. The reverse isn’t always true. So a 60W bulb in a 100W socket is fine. A 100W bulb in a 60W fixture is not.
My wife put a 75 W bulb in a desk lamp rated for 60 W. After about 10 minutes it stunk up the room. Apparently, the heated generated by the 75 W bulb was enough to “cook” the paint on the inside of the fixture, thereby causing it to outgas at a high rate. It’s not a problem with a 60 W bulb.
I “overclocked” a desk lamp with an integral plastic shade once and cooked the damn thing right into warpage. The whole one side just melted into a chaotic mass of plastic.
Household wall/ceiling sockets should all be quite OK with anything up through 150 watts (i.e., any “normal” bulb on the market). The one problem might be if more powerful bulbs would combine with a power-hungry appliance on the same circuit to blow a fuse/trip a circuit breaker when all are operating together.
Where you will run into problems is in lamps. When they recommend a maximum, there’s generally a good reason – jayjay’s experience is typical, and I can say that we had much the same thing happen. Usually you can get away with a 75 watt bulb in a 60-watt-max. receptacle – but you are taking a risk in doing that.
There are advantages in using a lower-wattage bulb, too. My experience is that they tend to last somewhat longer, and your power usage is reduced – not by a whole lot, but it builds up over multiple fixtures and multiple months. For example, at our previous home the shower was built into an alcove with a light fixture in the ceiling in the alcove just outside the shower (about overhead from where you would dry yourself after exiting the shower). That really only needs a 40-watt bulb – for that tiny little area (shower stall and about the same amount of space in the alcove outside the shower) that throws enough light for normal visionn, and nobody is going to be reading fine print or doing petit point in the shower! On the other hand, what lit the entire living room was one ceiling fixture, where a 100 watt bulb was essential to avoid having the half of the room farthest from it be somewhat gloomy.