I'm new to circuits and in a side project I'm trying to design a DC circuit without microcontrollers that will turn on an LED if a certain voltage range is detected. For example the LED turns on if there's a voltage over 1.2V on a certain node. I'm not sure what component or setup will be able to trigger at a threshold. I'm not familiar with most EE components beside the very basic ones (resistors, capacitors, inductors), but I would definitely like to know which ones I would need to look into to make this.
While Reinderien's answer is technically correct, you might want to have more flexibility when defining your voltage window. You might find the following circuit more satisfying:
This contains 2 essential building blocks: comparators, and AND gates. Vref (high) and Vref (low) are defined by potentiometers (R1 and R2). They're essentially knobs you can use to tune voltages.
OPA3 and OPA4 are voltage comparators; OPA3 is essentially a '<' operator and OPA4 is essentially a '>' operator. The component on the right is an AND gate. If both the input voltages coming in are high, the Vout is high. If one or neither is high, Vout is low. The result is the circuit implementation of the following pseudocode:
Vout = (Vin > Vref_low && Vin < Vref_high).