Can I run Incandescent and LED lights together?

September 20, 2011


This is a question we see on a fairly regular basis.

This is an interesting question and depending on the lights you are considering the answer could be yes .. or no.

The answer is dependent on how the lights you are looking at are wired and connected together – whether they are in series or parallel.

Mini Lights or Pre-wired LED lights wired in series

More often than not, people ask this question regarding string lights – mini lights. These lights are run in series and are at constant current through all the sets. Since the traditional incandescent lights have a much higher current draw than LED sets they will damage your LED lights.

Do NOT run LED and incandescent string lights in series.  Ever.  We also suggest that you plug your LED lights into a surge protector whether installed inside or out.

So part of the answer to the question is… “No”, you can’t run traditional incandescent and LED string lights in series in the same electrical run.

Bulbs and Cords wired in Parallel

But what about C7 or C9 bulbs? (Like these. These are the large Christmas light bulbs that are usually sold separately from their cords and you install them yoursef.)

This is the second most common way folks ask about combining incandescent and LED lighting. Eighteen-gauge C7 and C9 Christmas light cord is wired in parallel – so all the bulbs have constant voltage and variable current – each bulb only pulls the current that it “needs” – determined by its resistance.

This is the reason you can cut them to fit and skip sockets where you want to. So, in this instance, the answer is “Yes, you can mix the bulb styles”.

In parallel wired C7 and C9 stringers, you can mix incandescent and LED bulbs to your heart’s content… beyond the electrical specifications, taste and Christmas light decorum are your biggest considerations when mixing bulb colors and styles.

10 thoughts on “Can I run Incandescent and LED lights together?”

  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;

      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.

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