When a light bulb burns out, most people simply grab whatever spare lightbulb is available. If the old lightbulb was a little too dim, they might opt for a higher-wattage bulb to improve the illumination. There is potential 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 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.
Symptoms to Watch For
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 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.
Remove the mounting screws, pull the light fixture away from the electrical box, and inspect the wires inside. If you see melted or scorched wire nuts or insulation on the wire leads, circuit wires, or cable sheathing, there's been some serious damage and you should have an electrician inspect things. He will probably cut away damaged wires and reconnect them properly. The electrician will know if the light fixture itself has been damaged and requires replacement.
A table or floor lamp is also susceptible to damage from light bulbs that are larger than they should be. If the shade on a lamp is hot to the touch or has become damaged by heat, inspect the light bulb wattages and make sure they match the socket ratings. If the sockets themselves are scorched, they will need to be replaced. And while you're at it, make sure the lamp wire itself has not been damaged; rewire the lamp if necessary.
Choosing the proper light bulbs is a simple matter of comparing the wattages of the light fixture and the light bulb.
Find Wattage Rating of Light Fixture
Generally speaking, the maximum wattage ratings are printed on the light-bulb sockets of the light fixture or lamp. You will see language that reads something like: "Caution: Use only Type A lamp, maximum 60 watts."
In some cases where a fixture has two or more light bulbs, there may be a total wattage rating for the entire fixture. This may be printed on a small sticker somewhere on the light fixture, often on the insulation or baseplate beneath the fixture's globe. In this case, you'll need to make sure that the total wattage of all the light bulbs added together does not exceed the maximum rating of the light fixture. The goal here is to make sure that the combined heat of all light bulbs is not enough to damage the light fixture or penetrate through the insulation.
Find Wattage Rating of Light Bulbs
All light bulbs, whether they are traditional incandescent bulbs, fluorescent bulbs (CFUs) or LED (light-emitting diode) bulbs will have a wattage rating printed somewhere on the glass or on the metal collar of the bulb.
Compact fluorescent (CF) and light-emitting diode (LED) light bulbs that have begun to replace incandescent bulbs are usually labeled in a manner that tells you how they compare to standard light bulbs. The packaging usually says something like "75 watts (uses only 11 watts)." For purposes of matching light-bulb wattage to socket ratings, it is the smaller, actual wattage ratings of CF and LED bulbs you need to be concerned with. In other words, if you have a lamp with maximum socket ratings of 60 watts but find that you don't have enough light in the room, replacing the incandescent light bulbs with "75 watts" LED bulbs that use only 11 watts is a perfectly safe practice.
Do not think, however, that CF or LED light bulbs do not emit any heat at all. While the glass bulb itself is considerably cooler to the touch than standard incandescent bulbs, the metal base on these bulbs does get quite warm. Generally speaking, though, CF or LED bulbs with standard screw-in ends can safely be used with standard light fixture sockets (known as Edison sockets).
Choose Safe Bulbs
The critical factor is to make sure that the light bulb (or bulbs) inserted into a light fixture or lamp does not exceed the maximum wattage rating of the fixture. This requires you to inspect the light socket itself to identify its maximum wattage rating and choose a light bulb that is equal to, or less than, this rating. And with fixtures that have multiple bulbs, you need to make sure that the total combined wattage of the bulbs does not exceed the maximum wattage rating of the light fixture or lamp.
There are many reasons to make the shift away from traditional incandescent light bulbs toward LED bulbs. Prices of LED bulbs have fallen dramatically, and the quality of the light is now far better. LEDs now produce a light quite comparable to natural daylight, and the per-watt illumination is far better than any other type of light bulb. These are the best choice if you are concerned about energy usage. Best of all, most LED bulbs can be expected to last many years. Even when used 12 hours a day, an LED bulb can last up to 11 years.