To have only one spot of light centered where the hot-end supplies its stuff, I defined holes for the leds all converging to a central point located at the center of the ring, and about 10mm under it.To reduce power wasting, and heat dissipated in a resistor, I choose to connect the leds in a serial manner, rather than in parallel, as shown in the second picture. Each white led has a dropout voltage of 2.6v. The whole set has a dropout voltage of 10.4v. The common current is about 20mA. The resitor needed to reduce 12v to 10.4v, with a 20mA current is about 100 ohms. And the power dissipated remains very small.If you use led of standard colors, the dropout voltage is smaller, around 1.4v. You have to change the resistor value according to the new global dropout voltage.