This is what my husband (Master Electrician) had to say when I asked
him your question:
The LED voltage drop is about 1/2 volt per LED. Practical
applications would be for broaches or pendents. The typical circuit
current would be 10 to 20 Milliamps depending on how bright the
intended LEDs are to be. I would suggest using several LEDs in series
so their combined voltage drop is slightly less than the battery
voltage. I suggest you do not use a voltage dropping resistor in
series as this wastes your available battery life. The LEDs are a DC
device so for your tests, make sure you have all LEDs connected
properly for polarity or your circuit will not operate. Switches for
low voltage applications fail to operate properly when they get even
slightly dirty. I would suggest using a sealed, miniature magnetic
reed switch. This is impervious to dirt and moisture and will close
or open with a small magnet which could be part 2 of your artwork.
When it is removed, from back or front, the circuit will shut off for
Finally, do use a voltage dropping resistor and a Milliammeter to
check current. Test different combinations of LEDs until the right
amount and type of LEDs are found so a series resistor is not
required while not exceeding the current specifications of the LEDs.
If you do exceed the current spec. you will burn out at least one LED
and damage some of the others in the circuit.
Karen Bahr - Karen’s Artworx
Calgary, Alberta, Canada