The #1 question we receive is “If one bulb burns out, do the remaining bulbs stay lit?” The short answer to this question is yes, the bulbs do stay lit when one bulb burns out.
The problem is this is the WRONG question. The better question is: “If one bulb is removed, shorts out or breaks, do the remaining bulbs stay lit?”
I predict that 90% of the light strands sold in the USA will stay lit when a bulb burns out. In my experience, when light strands have issues; the strand has one bulb that is either shorted or is damaged in some way. Most light strands will fail when the bulb shorts or is damaged.
The ability for the light strand to stay lit when bulbs are removed, shorted or broken is a function of the light strand not the light bulb. There are two methods to accomplish this feat. The preferred method utilizes technology in each socket that regulates power to each socket. This method is the most expensive but to me it is the most reliable.
A less expensive technique that is popular in big box retailers uses a single “fuse bulb” which is always the first bulb in the stand. This fuse bulb cannot be removed from the strand; it is permanently installed. If this bulb is broken or shorts out, the entire strand goes out and cannot be repaired. Previously, it was easy to spot these fuse bulbs as the bulbs were about 50% larger than normal bulbs but now the fuse bulbs are about the same size as a normal bulb.
How do you know what type of light strand you are buying?
Ask the sales person “If one bulb is removed from the strand, will the remaining bulbs stay lit?”.
If the answer is yes, then ask “How is that done? Does the strand use a chip in each socket or does it use a fuse bulb?” If the person looks at your with a blank stare or there is an uncomfortable pause on the other end of the phone, it is highly likely a fuse bulb.
In conclusion, when considering light strands; ask the seller what happens if a light bulb is removed from the strand.
Click Choosing the Correct Lights for Your Christmas Tree to watch a 4 minute video demonstration of the differences among mini-light strands.