How to Tell the Difference Between Indoor and Outdoor Christmas Lights

A tangle of multi-colored Christmas lights.

While many lights these days are made for both indoor and outdoor use, outdoor Christmas lights are different from indoor lights in a few ways. It’s important to know which differences exist between the two, so you don’t run into any avoidable problems as a result of using the wrong lights.

Safety Tags of Indoor vs. Outdoor Christmas Lights

The Underwriters Laboratories, or UL, inspects electric products made in the United States. If a product is proven to be safe from shock and fire, it becomes UL listed. When purchasing indoor or outdoor Christmas lights, you should always make sure they are all UL listed and have the tags on the cord to prove it. If not, you could be in danger of electrocution or at risk of a fire in your home.

Indoor Christmas lights will have a green UL listed tag, or a silver tag with the “UL” written in green. Christmas lights approved for the outdoors will have the UL listed tag in red, or silver with red writing. So, if you have strings of lights from previous years and you cannot remember whether they are safe for outdoor use, just check these tags and they can tell you. If the UL tag is missing, do not take the risk. Restrict those strings to indoor use only.


Although this doesn’t hold true for newer Christmas lights, if you’ve managed to save some older strings, you will notice that lights meant for outside use will have bigger, stronger bulbs than those meant for the tree. As your older lights stop working and have to be replaced, this will no longer be an identifier of the different types.

Where to Use Them

It's becoming increasingly common for all Christmas lights to be approved for indoor/outdoor use. However, some indoor lights are still single-purpose, and if you use these Christmas lights outside, they will not be as resistant to any moisture. Rain, ice, snow, and even just condensation can get into the connections and cause an electric short that could damage the lights. If these lights are hung closer to the house, the short could also potentially start a fire. Bulbs on strands of indoor Christmas lights are also sometimes not as durable as those used in outdoor or indoor/outdoor lights and they can wear down more easily and break due to inclement weather.

Fortunately for lovers of Christmas lights, finding multipurpose lights is not much of a challenge. If you want to never worry about where you can and cannot string your lights, search specifically for indoor/outdoor varieties and eliminate the headache.

Indoor and Outdoor Christmas Lights FAQ

Can outdoor Christmas lights be used indoors?

Outdoor Christmas lights are designed for outdoor use and indoor lights are made for indoor use, so it's best not to overlap these purposes. Technically, outdoor lights can be used indoors because the lights themselves can't be damaged by the environment of your home.

However, outdoor lights might get much hotter than lights that are designed for indoor use. This makes them a potential fire hazard.

If you're using outdoor lights inside, check them frequently to see how hot they get.

What is the symbol for outdoor Christmas lights?

If you look at the boxes for Christmas lights, you will see certain codes and symbols that tell you how and where these lights are meant to be used. Lights that can be used outside will have a water drop symbol on them, indicating that they are resistant to water damage.

Outdoor lights might also be marked with an IP code. These are IPX3, IPX4, IPX5, and IPX7.

These codes simply describe different levels of water safety for the lights. The IPX7 lights are rated as watertight.

What happens if you use indoor battery operated lights outside?

Some battery-operated lights are rated for outdoor use but some are not. If you are trying to use battery-powered lights that are not rated for outdoor use outside, it is likely the lights will be damaged by water, ice, or snow.

Is it OK to use indoor light bulbs outside?

Indoor light bulbs are made for protective home environments, which means they do not have any degree of water resistance. If you use indoor lights outside, they are going to become damaged by the water and weather and will not last very long.

Are LED lights OK for outside?

LED lights are highly durable, bright lights and they have become a popular option in holiday lighting designs. If the lights are properly sealed and rated for outdoor use, they are safe to use outdoors.

No matter what type of light it may be, no matter the type of weather you may have, always and only use lights that are rated for outdoor use outdoors.