LED current regulation in several parallel strings of LEDs

[joecrow]

What is the negative effect of simply driving the LEDs with a power source and current limiting resistors? (In general, why are constant current regulators necessary to drive LEDs?)

 

[Audioguru]

1) One LED part number has a range of forward voltages. If you use a simple resistor then some LEDs will have a higher current (and higher brightness) than others. The ones with the higher current might burn out.
2) The power supply might not be regulated and have a voltage that is too high sometimes. Then the current will also be too high sometimes if a simple resistor is used then the LEDs burn out.
3) A battery might be used instead of a power supply. If a simple resistor is used then the LEDs will get dimmer and dimmer as the battery voltage runs down.

A current regulator solves these problems.