LED light intensity drop using 200k range resistors.
By consulting the LED's datasheet's forward current/voltage and luminous intensity/forward current curves:



Source: https://cdn-shop.adafruit.com/datasheets/WP7113SRD-D.pdf

Now, by calculating the current through the LED:


I = ( 9V - V(LED)) / R


You can then look up that current on the luminous intensity chart to get the luminous intensity as a percentage of the value given for 20 mA; on this datasheet it is given as 250 mcd.