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Any coating, such as paint and marker ink, on the LED lens is going to trap heat. Keep that in mind, because heat is the enemy of electronics like this. When I was in electronics class in high school we were taught to use a heat sink on the leads of an LED in order to prevent heat from reaching the ends of the cathode and anode; while soldering. That kind of heat ruins it fast (260-400 degrees F)The normal heat it produces will wear it out over it's lifetime. Trapping any extra heat, raising the internal temperature, will shorten the life exponentially.
remember that these commercially available bulbs are not suitable for fully enclosed fixtures because they can catch fire. Coating the bulb would trap extra heat, so be careful about it. You might do better to make a vented lens to put in front.
Current is drawn by LEDS to cross a gap. The current won't climb higher than it can achieve in the materials provided. It is the voltage that will affect current draw. Lower volts mean more amps, and too low means no arc. A voltage regulator and a rectifier are all that most LED "drivers" contain. If the LEDS are dim, it's because you are having voltage drop from length of run or excess LEDS, or the power supply is too small. Adding a resistor to the circuit will surely increase the total amperage.