Hi folks - still tinkering with some Christmas lights this season. Have a string of 50 lights on a small tree. No tags/labels on the existing string of lights, but I'm assuming it's 2.5v .42w bulbs as would be pretty standard. I'm grabbing some bulbs from another string of 100 lights (2x50 light segments, which is also 2.5v .42w bulbs). The bulbs work in the shorter 50 light string, but they are super bright - the same replacement bulbs shine much brighter on the shorter 50 light string than they do on the 100 light string. They are too bright on the 50 light string - so what am I missing?

I hope my explanation makes sense - happy to provide more detail.

At first I was thinking maybe I need 2.5v but lower wattage than the typical .42w - but again the same bulbs shine much brighter on the shorter string than on the 2x50 (100) light string.

Thank you!
BSN in Mass.

 

In the string where the few replacements were too bright you actually want higher wattage replacements.

The specific bulbs that are too bright are of a lower watt or amperage rating and in the present string are receiving more than 2.5 volts while the other bulbs are receiving less than 2.5 volts. The excessively bright bulbs will have a much shorter lifetime.

The above fact is not well known to consumers.

The incandescent mini Christmas lights of years past came in at least two wattages, regular (lesser wattage) and super bright (greater wattage).. If you put one or a few super brights in a string of regulars the super brights would not be super bright and might be dimmer than the rest. If you put a regular in a string of super brights the regular would be brighter(!)

In addition they made 3.5 volt replacement bulbs (also in super bright and regular and perhaps more variations) for 35 light strings, the 2.5 volt ones were for 50 light strings as you said.

The actual wattage of all of the bulbs in all of the strings is as of this moment unknown. You will need to use test equipment to figure it out and ultimately all 50 of the bulbs in any given string (each substring in the 2 x 50 light string) have to be the same for proper operation and bulb life. They can all be a little more than .42 watts each or they can all be a little less than .42 watts each..

One possible test uses your multimeter and a single AA or C or D battery cell. Do not use 9 volt batteries!

Connect up battery to meter, meter to bulb.. Set the meter to amperes then momentarily connect the other contact of the bulb to the other end of the battery. Read off the amperes. Because you are using 1.5 volts instead of 2.5 or 3.5 the amperes reading will not be correct compared for the amperes drawn while in the string of 50. But you are interested in the amperes reading for one single bulb relative to another single bulb, not the absolute number of amperes drawn. Test a few bulbs from each string and from each pack of spares and label the bulbs as to where they came from and put them in different piles depending on the amperes you read for the preceding test. Now you should have enough information to put the proper kind of bulbs in each string.

If you repeat the above test using correct voltages of 2.5 or whatever, write the numbers on a different sheet of paper from when you conducted the test with one 1.5 volt battery cell, and do not mix up the groups of numbers.

When you are done measuring amperes, immediately turn off the meter and if applicable unplug the meter wire from the meter body terminal marked A or amperes. If you try to measure volts with the meter set for amperes, you will fry the meter, possibly producing a large frightening spark.

 

Amazing info - thank you! I will figure out how to test bulbs for voltage and amperage. I have a multimeter but it might be only AC.

This string of lights is probably at least 15 years old - perhaps 20.

Thank you!

 

Also - actually are you saying that if the bulbs are all the same (let's say I replace them all with 2.5v and .42w) then they might all glow with proper brightness?

Of course you might wonder why I'm going through this trouble instead of just using a new string of 50 for our little tree. I like the long extension of wire on this string between the plug and the first light, and I can't seem to find a replacement with this similar length of wire.

Thanks!

 

Yes, if you replace all of the bulbs with a new batch of bulbs that are the same (volts, watts) within the batch then you will get uniform light.

 

Okay. thanks. Yes - uniform, but I'm sorry I also meant to ask would they all be super bright or when they are all the same bulb it would be normal brightness. Again assume I'd replace with all 2.5v .42w. (which currently burn super bright among the otherwise unknown bulbs)