Can I use non-dimmable LEDs on their own or with dimmable LEDs in an electrical circuit controlled by a dimmer unit?
No. Non-dimmable LEDs have internal power supplies intended to work over a voltage range indicated on the carton/product in order to work in various countries with a different national electrical voltage.
The internal power supplies are intended to maintain a constant output illumination level from the LED irrespective of the input voltage.
In simple terms varying the input voltage to the LED (via the dimmer) will result in the internal power supply within the LED trying to maintain a constant output.
In practice it is more complicated as the dimmer unit produces a non standard voltage that the internal power supply of the LED is not intended to operate with resulting in flickering, flashing and audible noises.
Operation will result in damage to the LED lamp, the dimmer or possibly the electrical circuit and should NOT be continued.