Replace 12V DC lighting with LED

You need to know which LED's you plan on using.

Also, LED's are polarized which means they'll only work in one direction.. Any ways.

Assuming you have some common LED which could be around 1.7 volt of a drop, lets say 25 ma's of drain on the power source.

Taking your 12 volts into consideration, you would need a resistor to drop the current to the diode.

R = (SourceVoltage-LEDVoltage)/LEDcurrent = (12-1.7) / 0.025 = 412 Ohms.

Wattage needed for this. W = (12-1.7) * 0.025 = 0.2575

I think a generic 1/4 R should work for this.

----- You can place these diodes in series. assume you use 4 in series 6*1.7 = 10.2 volts required..

You need to keep the required voltage below what your supply voltage is because the diodes need current flowing through them.. Now with this, you can use a different value R in series.

R := (12-10.2)/0.025 = 72 ohms..

A note that you should know, the closer you get to the source voltage using mulitple LEDS in series and lowing the R value, the more shoft of brightness you're going to see when the battery voltage starts to drop.

So you may want to use a lower series count of LEDS into an array cluster.

It's likely that an RV or boat dealer can get you a variety of LED or other (fluorescent) fixtures and lamps. Buying is the easy route here. I've seen auto lamps that are bayonet-mount dropin replacements for incandescent bulbs.

If you must build, be aware that low-power lighting (like, 1W or less) can be done with an LED flashlight lamp, available in the $5-or-under range, and high power (like, 10W) requires an array of devices, and probably requires a bit of 'ballast' design work. Switching power supplies and linear regulators and simple power-wasting resistors all have their place, you'll need to study all the alternatives, if only to eliminate them.

The '12V' power is NOT clean and reliable, you will want all your work to survive brief 50V spikes and various kinds of brownout and overvoltage.

What are you crapping on about ?

..... Phil

It would be smarter to just buy finished goods that fit what exists.

...and you can get finished goods from about a billion other places