Electronic – Pulse Dimming to 1-10V

The light output of an incandescent bulb depends upon its temperature (black body radiation). This is not the case with LEDs that emit photons of a particular energy - more photons more light.

Depending on the method used to control the light output you will get different results.

PWM generally gives better control and works well with LEDs. Some controllers may simply be limiting current by controlling the series resistance or the voltage supplied.

PWM with incandescent bulbs works well up to the point so little power is being fed into the bulb that it fails to achieve sufficient temperature to radiate light - most of the energy is now infra red.

A potentiometer is also called a variable resistor and rheostat. Those 100Ω ballast resistors and the potentiometer are the same as a "Resistive dimmer". They will not damage an led. They are the simplest way to control the current to a led segment.

Each of your 100Ω resistors are limiting current to ((12V - 1.35V - 1.35V) / 100Ω)) 93 mA and dissipating ~0.86W each (I hope they are 1W resistors, or they will heat up and fry quickly). Combined, that is 6.88W in heat for the resistors, and 744 mA. That's essentially a 12.5Ω load. Since the leds are pretty low forward voltage, and the resistors are burning a very large amount in comparison (2.7V vs 9.3V), you have plenty of headroom to change the resistance. Increasing the resistance lowers the current, which in turn dims the leds.

A single 10Ω 5W resistor will (roughly) halve the current (51mA) and brightness to each led, and since it is also taking up ~1/2 of the power, will help dissipate the heat nicely, as each of the 100Ω resistors will only be dissipating 0.44W instead of 0.86W. I saw 10Ω instead of 12.5Ω, as a 10Ω will be easier to find. You could use a 20Ω for 35mA to each led string. Or a 5Ω for 66mA each. Since leds are logrithmic, it's not an exact scaling of brightness.

Add a multi-throw switch, and you can chose between them.

^{simulate this circuit – Schematic created using CircuitLab}

The reason you fried your pot was that it couldn't handle your poorly designed panel. Frankly, you should have just stuck them all in series with a single resistor. 12V Source Voltage - 10.8V Forward Voltage (1.35 * 8) = 1.2V to drop. 1.2V / .093A = 12.9Ω. 1.2V * 0.093A = 0.111W. A single ~13Ω 1/4W resistor would have been perfect to set the upper limit and Most pots could handle a measly 1/4th~1/8 Watt.

^{simulate this circuit}