A light bulb burns out. You buy a new one that fits the socket, throw the switch and boom! The room lights up. Problem solved, right?

Maybe. It’s also possible that you’ve created a whole new problem. Just because a bulb is the same size and screws into a socket with ease doesn’t mean it’s the right bulb.

Who knew?

Choosing the wrong light bulb can create a serious electrical hazard, it could even lead to a house fire.

Figuring out what’s watt

The problem lies in how we think about incandescent bulbs and their wattages. More watts means more light, or so we believe. In fact, a watt is not a measurement of brightness but of power being drawn down an electrical wire. (If you want to measure brightness, use lumens, but that’s another discussion.)

We think in watts when it comes to brightness because — naturally — more energy down the wire results in a brighter bulb. It also means a hotter bulb. That’s why UL, which tests light fixtures and many other products, requires lamp manufacturers to mark the socket for a particular wattage.

If the label calls for a 60-watt blub, a 100-watt bulb will still fit, but it’s going to be a lot hotter inside the enclosed fixture. That can damage the fixture and even the wiring in the wall. Your household wiring, if it’s up to code, can easily handle a lot more wattage — but not if the wires’ coating is melted off.

A couple of hundred-watt light bulbs in one fixture and it can go over 90 degrees Celsius quickly, UL says over time the light bakes the plastic off the wire. Ninety degrees Celsius is 194 degrees Fahrenheit, hot enough to reheat dinner. Plastics, and some wire insulation, can melt at much lower temperatures.

Related: How to Dispose of Lightbulbs and 9 Other Hazardous Items

When it tests fixtures, UL often advises manufacturers to make changes to lessen the risk from heat build-up. For instance, some manufacturers install insulation inside the lamp to stop heat from affecting wiring. The insulation might have a reflective foil on it, too.

But there’s nothing to stop consumers from using the wrong bulb, beyond a little education.

LEDS: More light for less energy

So you want more light from your lamp or ceiling fixture but are smart enough not to use a higher-wattage bulb. What’s the answer? Consider an LED bulb. Yes, you can put one of these into a regular lamp. An LED bulb that says it produces the light equivalent of a 60-watt incandescent bulb is actually drawing far fewer watts of electrical power, Drengenberg notes.

Related: Ask the Expert: CFL and LED Lightbulbs

The packaging will say, “This is a 60-watt light bulb” but in smaller print it will say 13 watts. It replaces a 60 watt bulb but it only draws 13 watts. It’s usually roughly a 4-to-1 to ratio.

Drawing less watts means less heat. You can easily touch an LED bulb, for instance, even if it has been burning for some time. One LED bulb on the market that produces the equivalent light of a 100-watt incandescent draws just 18 watts of power. Two of them in a fixture rated at 40 watts per socket won’t heat up enough to matter, and they’ll last for years and years.

Want some help deciding which bulbs to buy? LightSmart, an app from UL, lets you upload pictures of the rooms in your home, shows you the effects of different bulbs on the room lighting and even calculates cost of ownership based on regional utility rates.

In the meantime, you won’t go wrong by following the instructions on your lamp or light fixture. Don’t surpass the recommended watts limit, and everything will be illuminated. Safely.

Related: 6 Smarter Ways to Light Up Your Home

Greg writes about personal finance, business and technology. His work has appeared in Businessweek, Newsweek, Forbes, Bankrate and a variety of trade ​publications.