When a bulb burns out, most people simply grab whatever spare light bulb is available. If the old light bulb was a little too dim, they might opt for a higher-wattage bulb to improve the illumination. There is danger here, however, because light fixtures carry a maximum wattage rating, and if bulbs are installed that exceed this rating, there is the potential for overheating the fixture.
The Potential Danger
Installing light bulbs with wattage ratings that are higher than the fixture ratings does not necessarily damage the electrical circuit wires, nor is it likely to cause a circuit breaker to trip or cause other problems to the house wiring. The potential danger usually lies in the fixture itself. Light fixtures have wire leads that are attached to the circuit wiring, and the heat that is naturally generated by a light bulb can cause these wire leads to overheat and possibly melt the insulation on the leads.
Some light fixtures have internal insulation that is designed to shield the wires up to a certain temperature. If this temperature limit is exceeded by operating the fixture with bulbs that are too large, damage to the wiring can occur. In the case of recessed light fixtures (can lights), the trapped heat can even overheat and scorch wood framing members.
This potential danger exists both with hard-wired light fixtures mounted in a ceiling or wall sconce, as well as with plug-in lamps.
Before You Begin
Anytime you detect a burning odor or see scorch marks on a light fixture or lamp, it’s a sign you may be exceeding the wattage rating of the light fixture. Shut off the light and turn off the power at the breaker or fuse. If it’s a lamp, unplug it.
Then have an up-close look at the fixture. If it feels very warm to the touch, that’s a danger sign. At this point, it’s not enough just to replace the bulb with one of lower wattage—you also need to check to make sure that permanent damage hasn’t already occurred.
Source: The Spruce