Change the voltage of the LED, below 4v because it is the supply voltage
Calculation:
Vbb=Vcc=4V
Ic=10mA, β=100
Just by using a perfect resistor on base and adjusting base current, we can decide the Collector current
β=Ic/Ib, since we know Ic and β,
Ib=Ic/β=10mA/100=100μA
Now, Rb(the base resistor) =(Vbb-Vbe) /Ib
=(4V-0.8v) /100μA=32kΩ
Since the Vbb is close to the knee voltage of silicon diode approximately 0.7V, i chose 0.8V
Now if you vary the Vled from 1v to 4V, The LED won't breakdown
Don't vary the Vbb voltage, just change the Led turn on voltage or knee voltage
