I have two buffer stops with lantern now if an LED is inserted into the lantern and power taken from the track (20v) I assume the LED will flash (but not noticeable) but I also assume track power will blow the LED how would I get around this?
Yes, in theory, it will 'flash', but the frequency is such that you will not notice it..
It is frowned upon, to reverse-bias a LED (for the half-cycle it is 'off') but it should not do any damage.
You need to limit the
current through the LED.. A 1K resistor should be adequate for this. - You can vary this, a little, if the LED is too dim or too bright.
If you are making the LED brighter, then you are increasing the current through it, so it would eventually fail if you reduce the resistor value too much.
Without knowing the specifications of your LED's, I would not go below 820 ohms. - Brighter.. It is better to use a 'high-intensity' LED that can be run at a lower current, then over-drive a standard LED.
To make the LED dimmer: Try values of 1.5 - 2.7 K.
K = kilo-ohm (1K = 1000 ohms)
HTH?
PhilP.