Hello!
If you want people to reply, you should consider sending a schematic of what you did. There
are many ways of wiring even a simple inverter. It depends whether the LED is connected
to the anode or to the cathode, it also depends on how the input is wired. What is your
interrupter? Is it a simple photoresistor? Do you associate it with a resistor at the input of
the gate or is there a more advanced circuitry between the detector and the gate?
If it does the opposite of what you want, it may be precisely because it's an inverter. In this
case use another gate serially (the 7414 has 6 of them).
Dora.