Two Channel (stereo) Control Voltage (CV) to LED circuit. Each channel can tolerate -5 to 5v. Positive CV is sent to the LED on the same channel. Negative voltage flips to positive and is sent to the opposite channel where it is summed with positive. LEDs are biased so that they come on at relatively low voltages and brighten as additional CV is applied. They max out at 30ma at the op amp rail of 9volts. DC or AC CV is tolerated in any combination. This is one half of an (optically isolated) vactrol stereo pan control for a synth. The other half uses LDRs placed next to these LEDs as pots to control gain for stereo amp circuits.
The circuit in the upper right is a LDR CV generator with an inverted and non-inverted output.
