Question about Christmas Lights Etc Toys

# How do I pick a right bulb for Christmas tree and string lights? Some are 2.5V some 3.5V some 5V... Some say 2.5-3.5v. I replaced some burned bulbs with generic 2.5-3.5V bulbs from stores and they are

Replacing bulbs with various ones. It seams there are different voltage bulbs, even when the same voltage rating, they have different power/currents/resistances

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If you are lucky, it is very simple. But then, it can get complicated.
Given that you are talking about classic incandescent (non-LED) bulbs:
Strings are made of certain number of bubs connected one after another (in line, daisy chained), so voltage is split among them. 10, 25, 35, 50 are common numbers. If your string has 75, 100, 150 or so, it is built with 2 or more groups of lights. I.e. two groups of 50 bulbs in-a-row. (two groups are connected in parallel, so both are getting 110V).
If in doubt, pull one bulb out and count how many bulbs turned off.
Divide 110V with how many lights you have in the string (one group) and that is an approximate voltage of each bulb.
50 pcs - 2.5V
35 pcs - 3.5V
20 pcs - 5V
10-12pcs - 12V
35-50 pcs in-row sets are most common. If you buy generic 2.5V-3.5V replacement bubs, they will work in any 35-50 pcs set. The brightness difference will be small.

You should replace the burned bulbs as soon as possible. Each bulb has what is called "anti-fuse". When it burns, it creates an open circuit. This means, that all 110V will show at the contacts of a burned bub. inside of the wire is aluminum wire wrapped about contacts that hold the filament. This wire is coated with oxide that acts as an insulator. 110V is enough to burn through the oxide insulator, and burned bulb gets bypassed, allowing other bulbs to stay on. However, as 110V is now divided to smaller number of bulbs, meaning each bulb gets higher voltage. After several bulbs are burned, the voltage becomes too high, and all of them burn.

This was an easy part. However, there are some differences when you look at different manufacturers and types of lights.
I.e., 2.5V bulb will usually draw 150mA at 2.5V. However, some longer strings, or strings with three groups of racing lights use
2.5V 100mA (0.25W) bulbs. If you believe your string should use 2.5V bulb, and replacement one is dim when installed, try 100mA bulbs. Search the web or eBay.
If you have similar problem with other voltages, and you don't remember exact model and manufacturer f lights (who keeps boxes anyway?) that you need to research different versions of certain voltage bulb. Again, Google it or eBay/Amazon, are good places to do it. takes some time to find the answer.

Another difference are Sylvania Stay-Lit lights. They don't use anti-fuse bulbs. Often, they use 2.5V 70mA bulbs. No aluminum wire inside. They are patented to stay lit even if you remove the bulb, or break it. Inside of the socket they have electronic circuit (thermistor I think) that "senses" missing or burned bulb, and takes over the current for other bulbs, with almost the same voltage drop/resistance, as the bulb would have. In this case, there is no risk for other bulbs to get higher voltage and burn.
I recommend to use proper replacement bulbs (with no anti-fuse). As a temp solution (if you want all bubs shining and it will take time for right replacement ones to arrive), bulbs with anti-fuse will work (i.e. 2.5V 100mA) but when/if those burn the aluminum wire inside makes a short, deceiving the purpose of stay-lit electronic circuit and puts more voltage/stress on other bulbs.

Hope this helps. Good luck!

Posted on Nov 30, 2014

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Now this is one I ask myself. Why Dont the same people who sell a certain brand of lights sell a pack of replacement bulbs of the same brand? Most lights come with a few replacement bulbs but it just seams easier to use and old set that match others I have for "spares bulbs" and buy a new set for a tree or bush or an item not next to other older set(s). Otherwise if you still have a bulb one can check the ohms with a multi-meter and compare the with another. Voltage would have to match and then would have to look for some bulb with the closest ohm. Like I said. Why not sell bulbs for the lights you have sold. Seems the cheap ones are the only ones that are more standard then bigger names cause they just seem to change (improve) their design. Good luck.

Posted on Nov 30, 2014

Hi,
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Posted on Jan 02, 2017

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