Darlington does not switch
You probably want R2 to be more like 68~100 ohms than 7K for a 500mA load, and R1 more like 510 ohms to 1K. That corresponds to a beta of around 10 for the PNP and 20 or so for the NPN. 

I presume there are many R3 or else you'd never see 500mA. 

Even with those values you should be able to see some light from the LEDs, so maybe something else is wrong.