The answer here begs another question. First off is this just a mental exercise or are you trying to do. Work? If what you are doing is to turn the led off an on this is a bad way to do it, because it uses current all the time and generates waste heat. Now if you are supplied with unlimited supply power this might not be an issue, although if your supply is a battery this is a whole different story, but it is still bad Engineering practice to use the circuit that you depict. It would be so much simpler to put the led and current limiting resistor in the return leg of the switching transistor then the control voltage simply turns on the transistor or not so the led is off or not. You would only have to make sure that the switching transistor will carry enough current to power the led. The control or Base resistance will depend upon what power that you have available for switching. The power input resistor depends upon how much the supply voltage has to be dropped to be in the correct working voltage of the transistor and the led. And of course whether you use a N or a P Channel switching transistor depends upon your supply voltage being Positive or Negative. This also determines which way you face your diode (led). Your switching voltages polarity must be sourced to your supply or it will have to be run through an inverter of some sort be it another simple transistor switch or inverter ic. Laurin Cavender WB4IVG

The answer here begs another question. First off is this just a mental exercise or are you trying to do. Work? If what you are doing is to turn the led off an on this is a bad way to do it, because it uses current all the time and generates waste heat. Now if you are supplied with unlimited supply power this might not be an issue, although if your supply is a battery this is a whole different story, but it is still bad Engineering practice to use the circuit that you depict. It would be so much simpler to put the led and current limiting resistor in the return leg of the switching transistor then the control voltage simply turns on the transistor or not so the led is off or not. You would only have to make sure that the switching transistor will carry enough current to power the led. The control or Base resistance will depend upon what power that you have available for switching. The power input resistor depends upon how much the supply voltage has to be dropped to be in the correct working voltage of the transistor and the led. And of course whether you use a N or a P Channel switching transistor depends upon your supply voltage being Positive or Negative. This also determines which way you face your diode (led). Your switching voltages polarity must be sourced to your supply or it will have to be run through an inverter of some sort be it another simple transistor switch or inverter ic.