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.