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LED Exponential Current Control

February 22, 2026

Human vision is better at noticing a small change in brightness for darker objects than lighter objects. This is a good thing, but it makes it harder to create a brightness controller.

A naive circuit for brightness control will use most of its range for bright values and very little for darker values. So it is very hard to set a dim value.

Most models of human vision uses gamma-correction to fix this, but it is hard to do using an analog electric circuit. Instead an exponential correction can provide a similar result.

I put together an LED control circuit to test this:

The circuit built on a breadboard:

Notes

I tried several resistors and potentiometers to the input range for the exponential amplifier.

The LMV358 operational amplifier minimum output level is typically 120mV. This prevents it from generating a 0V control signal and to turn the LED fully off.

Voltage ranges:

Location	Range	Inverted
Potentiometer	2.78 - 2.98 V
Exponential amplifier	2.47 - 0.20 V	Yes
Inverting amplifier	0.10 - 2.28 V
Current control input	0.04 - 0.91 V

References

1. Gamma correction, Wikipedia. https://en.wikipedia.org/wiki/Gamma_correction
2. LMV358 Operational Amplifier, Texas Instruments. https://www.ti.com/product/LMV358
3. 1N4003 Diode, Diotec Semiconductor. https://diotec.com/en/product/1N4003.html
4. BC548 NPN Bipolar transistor, Wikipedia. https://en.wikipedia.org/wiki/BC548

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