Analyzing Opamp circuits
You can simulate this with falstad.com/circuit and clearly see what happens
I've build it already for you just play with the slider for Vref and see what happens.

When Vref = -1V then there has to be -1V over (-) of the opamp
to get this the opamp's output has to be negative so that a basis current can flow this current  comes from the emitter the colector current will be higher and the led will turn on

When Vref = +1V then Vemmitor should be 1V but this can never be achieved so the opamp's output will be  (+1V-(0A))* ampfactor => opamps max saturation voltage
So the transistor basis is high and there won't be any current flowing through the led

you can see it like this, in this particular circuit