I'm looking to put LEDs under the fretboard of a Les Paul style guitar. The fretboard already has plexiglass in it for the see-thru aspect. I'm looking for the best way to wire this, preferably with an internal battery pack with a switch mounted through the surface of the guitar. I'd like the battery pack to be rechargeable. The biggest concern is that it be efficient. I'd like to recharge without opening up the guitar and the switch should be accessible from the outside as well. I'm not an electricity guy, I don't know how much battery power I'll need to power LEDs. The LEDs will probably be in light bar form, as it needs to reach about halfway down the neck. Any hell would be great! Thanks!
If you don't know anything about electricity, you should probably give up on this idea.
1.You'd have to pull up the fretboard and hope it doesn't warp.
2.route out the inlays
3.route out a path for the leds
4.reattach the fretboard
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Well, fortunately for you, I am an electricity guy - actually, I'm an electronics technician. I'm not much into design, but I am into repair. Both design and repair use the same math, so here we go...

A couple of things you need to think about here. If you're using Li-Ion or NiMH batteries, you need to have some way to monitor their charge and cut it off, once they've reached a charged state. Connecting an unmonitored DC source to these cells will result in overcharging and you can stress the battery, or worse. So, you'll need a special charger, especially if you intend to leave them in the guitar and charge it without removal of the pack.

Efficiency... LEDs are fairly efficient devices. However, as we add more of them together, in either series or parallel, the current draw is going to increase. What we need to do is find out how many LEDs you need to accomplish your task, then add up the milliamps required by each to find the total drain on the cell, or battery pack.

Let's say we need 10 LEDs and the milliamp draw for each is 5 mA. That means each LED requires .005 A to produce adequate light. For the sake of this example, we'll also pretend that each LED requires 1.6 VDC. This could be designed using two parallel legs connected to a 9VDC battery. Each leg would have 5 LEDs and each leg would need a dropping resistor to protect the LEDs from too much current. We could use two 220 Ohm resistors rated for 1/8 Watt each - I'd probably go 1/4 Watt for a safety factor. According to my calculations, this would consume 9.1 mA. I consulted the chart for a Duracell Coppertop, which I realize is not rechargeable, but it'll give us a rough idea what we can expect from a similar rechargeable battery - at 10 mA draw, we could expect around 50 hours. I suspect in reality, we'd probably see less than that.

Not sure if this made sense. If not, feel free to PM me and I'll draw it out on paper and scan it to PDF or JPG and post it for you. It can sometimes make it clearer to see it on "paper."

Using lightbar LEDs is no different. We still need to figure out current draw, determine how many batteries are needed and figure out the dropping resistors. Depending on the number of LEDs in the lightbar, the current requirements could be up there, which will require a larger battery pack, which adds weight.

Feel free to ask any questions. I'll answer as time permits.