So many folks make mistakes in replacing miniature light bulbs, that I did a search for what you should know about replacing miniature bulbs. I found a list on The Yulelights Collection of critical things to do when replacing burned out bulbs.
- Don’t mix old and new bulbs! That’s because they each have different current ratings, and in a series wired string, current is important. For example, 12 volt bulbs from pre 1987 had a 90 milliamp current rating, while modern 12 V bulbs are 60 milliamps. If you mix both types in the same string, the bulb with the lower rating will burn out quickly. In some cases it will burn out in a brief flash! That’s why the bulbs have to be a matched set. So you can either search for old stock bulbs, or replace all the bulbs with modern ones.
- Always replace burned out bulbs promptly to prolong the life of the remaining bulbs.
- To determine the bulb voltage, first check the instructions on the back of the box, if you still have it. Then check any tags that may be attached to the string. Here’s a trick you can try. Remove one bulb from a working section of the set and then count how many bulbs go out. If 50 bulbs go out, then you need 2.5 volt bulbs. If 35 bulbs, it’s 3.5 volt. If 20 bulbs, it’s 6 volt. If 10 to 12 bulbs, you need 12 volt.
- When you install a replacement bulb, it should light with about the same brightness as the other bulbs in the string. If the new bulb is much brighter or dimmer, you probably have the wrong bulb. You may need to try different brands of bulbs to get the best match in brightness compared to the others.
- If you find more than half of the bulbs in a string are burned out, you should replace all of the bulbs as the remaining good bulbs will be severely stressed and will only last a short time anyway. (known as re-lamping)
- If you are re-lamping a set try to use all of the same brand of bulbs as different brands often have slightly different voltage/current ratings. This could cause one brand to burn out faster than the other.
- Old sets may use bulbs which are now obsolete. The only option is to replace all bulbs with modern equivalents. Just be sure to use bulbs with the same or higher voltage rating.