How about you use a proper LED DRIVER IC?
See
https://www.digikey.com/products/en/integrated-circuits-ics/pmic-led-drivers/745 for examples.
Plain leds are not controlled by voltage, the brightness is controlled by varying the amount of current going through the LED. There is a minimum forward voltage required for the LED to turn on, and there's a very narrow region of voltage where the LED may not be fully turned on, like let's say between 9v and 9.5v but once you go outside that region you must limit the current otherwise the led would be damaged.
The most basic way to limit current is by placing a resistor in series with the led, so that's what you may have on your "module".
A led driver IC starts with a low voltage and slowly ramps up the voltage until the leds connected to it start to light up and current flows through the LEDs ... a resistor is used to monitor the current and the led driver will constantly adjust the voltage up and down to maintain the current flowing through the leds at the level set.
Here's an example of a very efficient led driver IC :
https://www.digikey.com/product-detail/en/diodes-incorporated/AL8860WT-7/AL8860WT-7DICT-ND/6226981See page 2 of the datasheet where you can see how simple the circuit is:
https://www.diodes.com/assets/Datasheets/AL8860.pdfYou can set the maximum brightness by setting the maximum current (200mA) with a resistor, and then you can use the CTRL pin to adjust brightness easily.
For example, for the chip linked above, the maximum current is set with the formula Iout = 0.1 / Rs ... so Rs = 0.1 / Iout.
So, for 200mA you'd need Rs = 0.1 / 0.2A = 0.5 ohm, for 100 mA you'd need 1 ohm and for 50mA you'd need 2 ohm .... so you could have 0.5 ohm + 0.5 ohm + 1 ohm in series....
50mA : leave everything as is
100mA : use a switch to short out the 1 ohm resistor ... you're left with 1 ohm so you get 100mA
200mA : use switch to short out 0.5 ohm + 1 ohm, leaving you with only 0.5 ohm
Or, if you only need 2-3 thresholds/levels of brightness you can place multiple resistors in series which in total give you the resistance for the worst case scenario (maximum current) and then you can use a switch to short out particular resistors in the chain, reducing the overall resistance.
Drive to voltage below 0.2V to turn off output current
Drive with DC voltage (0.3V < CTRL< 2.5V) to adjust output current from 0 to 100% of IOUT_NOM
Drive with PWM signal from open-collector or open-drain transistor, to adjust output current.
Linear adjustment range from 1% to 100% of IOUT_NOMfor f < 500Hz
So for example the easiest super simplest would be to send a voltage on the control pin between 0.3v and 2.5v to adjust brightness.
The cheapest LM317 or 1117 linear regulator can get you 1.2v ...2.5v which should translate to 55%...100% of maximum current.
You can use a potentiometer instead of the adjustment resistor to set the voltage between 1.2v and 2.5v