Why did they use these resistors??

[hayaalsh]

This circut is used to make an electric feild motion sensor as shown in this link:https://www.elektronik-labor.de/Notizen/555LEDeng.html
My Question is, why do resisrtors (marked by red) have these values??

Thank you

 

[barry]

The 1M is the collector resistor for your darlington pair which I is simply working as a switch; the value is not really critical. Higher values will give lower current flow. The 100 ohm resistor limits the current into the LED so it doesn't get damaged by excessive current.