Help with simple LED switching circuit

Hi all,
I need help with a simple LED switching project, I have 2 LED's, 1 RED & 1 BLUE connected to a 6VDC power source, the BLUE LED acts as a standby indicator & the RED LED indicates full circuit saturation, what I need is for the BLUE LED to turn OFF when the RED LED ANODE receives power. I need it to be as simple as possible & I am thinking using transistors but not quite sure how to do it, any relevant suggestions would be appreciated. Thank you

Here are a list of forward voltages for different color LEDs. If yours are as published, this simple circuit should work.

Red is the current through the Red LED; Blue is is the current through the Blue LED as a function of the input voltage sw6V.

That's perfect, doesn't get much simpler than that, I initially failed to see the LED as a (light emitting) diode, but now I see what you've done. Thank you so much, I really do appreciate your help MikeMl. Cheers, Beers

The only catch is the threshold for switching is ~5V and not a logic level like 1.3V for TTL or V/2. for HCMOS.

The switch threshold depends on the difference in Vf of the LEDs below the value of the 6V supply.

Using HB LEDs Red is around 2~2.2 and Blue 3~3.2 so the difference is 1V, hence the threshold will be ~5V +/-0.3V with overlap and both ON during transition.

For margin the Vsw must be equal to the other supply.

Tony Stewart said:

...
For margin the Vsw must be equal to the other supply.

Click to expand...

Which is exactly what the simulation shows and the OP said he wanted, and is going to do!

Yes very good Full saturation <1V below V+

For Saturation, keep in mind BJT must have 10% base current to get rated Vsat.