Need help identifying the right resistor?

I have a DC battery (12volt, 5.1Ah AGM) an want to power longterm a single 5mm LED light (Intensity 7000mcd, FW current 25mA, FW supply 3.3V - 3.6V max), what are the specifications for the right resistor to use? Do I need a resistor on the positive side only, or positive and negative? Thank you in advance for any guidance you may provide. I am an artist trying to solve a technical challenge of illuminating a glass eye in a new piece of art that is almost finished. See attached image file (the eye is too dark, it needs to be illuminated from behind)

http://led.linear1.org/1led.wiz
has a calculator, try that. The resistor can go anywhere in the series circuit. This is not the case in all systems, but yours is fully "floating".
You can use two resistors of half the calculated value, and each will have half the power dissipation, etc.
Here is a battery life calculator,
http://www.digikey.co.nz/en/resources/convers...alculators/conversion-calculator-battery-life
you can find out how long the device will run for,
cheers,
Richard

This will work, thank you, thank you, thank you!

Resistors are devices used in electronic circuits to provide a known resistance to the flow of electrical signals. They are used to scale and shape the signal that is passing through them to help achieve the desired performance of the circuit. Since they are small and cylindrical, it would be difficult to print the resistance in a readable form on the cylindrical body. Instead, they are commonly marked with colored bands to indicate their resistive value. The bands are rings around the body of the device that when read will allow you to determine if the resistor value is correct for the desired shaping of the electrical signal. Use these tips to learn how to read resistors.

https://www.hvacpw.com/hvac-tools/hilmor-tools.html

Your information helped me find the solution, thank you. Attached is the finished piece of art.

No problem Paul, always interesting to see art and electronics intersect. Mind you, all I did was point you to some web sites,
cheers,
Richard