I am designing a device that will check whether a fuse box motherboard is outputting 12V or not. I first considered diodes as they each have a 2V drop so I had 6 in series and functioned well but having 6 LEDs is not efficient. I then considered a npn BJT and had no luck and now I have designed a differential OP Amp that turns on the LED if the Voltage is not 12V. I chose R1=R2 to be 10k ohms and R3=R4=20k ohms giving a gain of 2 I believe. This means that the 2V LED should turn on when the input is 11V or more. Will this work in turning the LED on if the voltage is not 12V? V1 will be the voltage from the output voltage from the fuse box needing to be measured and V2 is the 12V reference. I am also worried if it does work that the current through the diode will be strong enough as it is required that it is bright.