hi EM,
Look at this image.
E


EDIT:
Added an LTS sim, showing more realistic circuit values, than the values derived from assuming Vbe values of 0.7v.

 

hi EM,
Look at this image.
E
View attachment 167481

Thank you so much. Can you also help me answer my question which i asked in this thread recently regarding the graphs and all?

 

hi EM,
I have updated post #22, added a LTS sim.
If you rewrite your query regarding the graphs after reading post #22, I will try to answer that query.
E

 

hi EM,
I have updated post #22, added a LTS sim.
If you rewrite your query regarding the graphs after reading post #22, I will try to answer that query.
E

I really thank you for the patient explanation. Really helps me understand better now. Thanks a lot Eric

 

Yes, that is correct. If you reduce the voltage to the circuit at some voltage the LEDs will dim because there is not enough voltage to drive them at full current. Above the voltage at which the LEDs draw the intended current the transistor to which the LEDs are connected will begin to absorb "excess voltage" to limit the collector current to the value set by the resistor on the emitter of the transistor to which its collector is connected.

The transistor current source section of this article (URL below) goes into some detail.
http://hobby.dapj.com/2010/12/drive-led-with-constant-current.html

I am really getting good clarity by reading this reply again and again. Thanks