Can I run Incandescent and LED light strings together? (…in series with one another? …end to end?)

November 17, 2020

Short Answer: No

Longer Answer:

This is a common question. We are going to answer it in this post for light strings that are PRE-WIRED. We’ll answer this question for traditional C7/C9 cords that take either LED or glass bulbs in another blog post.

The types of lights referenced in this article are what you’d think of as Christmas tree lights.

Lights like these:  Incandescent Christmas tree string lights or the LED versions.

These light sets are manufactured in series and the same amount of current runs through all the light sets strung together.

And the more lights that are strung together, the more current they “pull” or require. (For more about Christmas lights wired in series vs. parallel head over here.)

Since the traditional incandescent lights have a much higher current draw than LED sets, pulling all that extra current through all the bulbs will damage your LED lights by either blowing their fuses or damaging the bulbs before ruining the light string.

In other words: Do NOT run LED and incandescent light strings plugged into each other. 

We also suggest that you plug your LED lights into a surge protector whether installed inside or out.

If you have a question about parallel wired Christmas light bulbs and cords, head to this blog post about mixing C7/C9 incandescent and LED bulbs on the same custom cord..

Article originally published September 20, 2011. Edited and re-released November 17, 2020

14 thoughts on “Can I run Incandescent and LED light strings together? (…in series with one another? …end to end?)”

  1. Actually, mini lights have a much LOWER resistance than LED lights and, therefore, draw the higher current: Ohm’s Law E=IR or I=E/R. Since E is constant, a smaller R means a larger I. For this reason, you can connect a string of mini light to the 110V supply and have enough current left over to connect a LED string in series with it, providing neither string is too long.

    1. It’s not an issue of required supply but of damaging the semiconductors.

      Since some LED light strings have as little as a .02 amp current draw (using one of our light strings as an example), the current pulled by the traditional mini lights will damage them.

      Run pre-wired LED and incandescent lights strings on completely different circuits from a splitter or different extension cords. We also suggest NOT mixing LED light strings from different vendors as variation in electrical specifications can make these incompatible with each other.

      We also remind folks to protect all of their LED products with surge protectors whether installed inside or out.

  2. I am gradually transitioning from incandescent Christmas mini-lights to LED versions, so at this point I have both. Looking at a given string of lights, I sometimes can’t tell which is which kind. I’ve been told incandescent are hot to the touch, and that they have visible filaments. Any other differentiators? The labels on the end of the strings don’t say which kind they are either. Thanks.

    1. Hi Randy,

      Sorry for my slow response!

      What you’ve been told is correct related to Christmas light strings. The key thing is the visible filament.

      Incandescent light bulbs are generally made of glass instead of plastic/polycarbonate.

      Incandescent bulbs have little wires popping out of the sides of the base of the bulbs. LED lights – if they are replaceable – don’t generally have the same style base but will be bigger and not have those little wires.

      There are large Edison-style bulbs that are glass and LED with mock filaments out there to confuse you but for smaller Christmas light style strings, looking for the filament is a good first step in differentiating between LED and incandescent.

      Check the specs as well. Incandescent Christmas lights will run about .5 watts per bulb for mini lights and 5, 7 or 10 watts per bulb for incandescent C7 or C9 bulbs.

      LED C7 or C9 bulbs are less than a watt per bulb as a rule of thumb.

      Hope these extra tips help.

  3. I read that you shouldn’t mix different brands of led because of electrical variations.. what do I look for when trying to match same size bulbs to different brands? Only asking because I just bought some on ebay to replace some lights without even thinking about it.. :-/

    1. The best thing in this situation is to purchase absolutely identical light sets if you are going to move bulbs out to repair existing sets.

      The nice thing with C7 and C9 separate bulbs and cords is that the bases are standard E12 or E17 — so it’s straightforward replacing bulbs and you can mix any style you like since 18 AWG Christmas light cords are wired in parallel.

      The parts that make up that type of light string is here;

      https://www.christmas-light-source.com/christmas-bulbs-cords

      I’m not sure if I’ve been any help with your ebay purchase…. consider using those lights strings on their own in a different project if they aren’t an exact match.

  4. I’ve been struggling to find the best replacement for the traditional look of a C9 incandescent bulb for the exterior of my home. All the C9 LED lights I’ve looked at or researched or either too dim or a ghastly yellow.

    Can I install red LED C9 bulbs and clear incandescent C9 bulbs on the same line as long as I’m careful of the cord length? This would give me the look I prefer and, when I find a C9 LED bulb with the “warm white color” I like, the incandescent can be swapped out in the future.

    1. Yes, you sure can alternate those bulbs on a traditional parallel wired C9 Christmas light cord. It’s a great workaround until you find an LED white bulb that has the look you are going for then they can easily be switched out.

  5. I am planning to rework my Christmas horse statues with LED rope lights. I did the sleigh several years ago with the incandescent ropes (red with white-looks great).

    Will I be able to plug the horses into the same covered remote 3 outlet extension cord as the sleigh?
    I run several heavy duty extensions in a line back to the house outlet.
    Or should I just go back to regular incandescent bulbs☹️

    1. Hello,

      We can’t give electrical advice but yes, you should be able to plug your horses and sleigh each into an extension cord end connector as long as you don’t exceed the cord’s maximum current rating. (Consider hiring a master electrician to come take a quick look at your setup.) Be sure not to run any displays in series with each other to avoid exceeding the current rating of any of the light strings or rope. (I hope that makes sense!)

      We would also like to encourage you to purchase one longer extension cord that is rated for the distance you are running instead of running several extension cords in a daisy chain. Again, an electrician can give you the wisest counsel. Running a more permanent electrical line with properly rated conduit, grounding, and a box with GFCI outlets might be a great next step for your Christmas light project.

      We have enjoyed working with both incandescent and LED rope light and strings. The energy efficiency of LED is going to be an advantage to you if you have a larger display and few available outlets.

      Hope this helps and let us know if you have any other questions.

      Shellie

    1. We suggest that you do not plug in different brands of lights especially with LED light strings, in particular. Unlike incandescent lights that can be “the same”, LED light strings can have various electrical differences that can make their electrical specifications very different. As a result, we strongly suggest you not run LED strings from different manufacturers in series with one another.

      Also, double-check your strings, even if they are from the same manufacturer, to make sure that they have the same electrical specifications before plugging them together end to end.

      Hope that helps.

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