555 timer in astable mode: How can I achieve longer low output than high?
The 555 can't be reduced under 50% duty (just with resistors, see below) since the discharge resistor has to be at less than half the value of the charge resistor (otherwise the junction of the two cannot reach the low trigger of 1/3 the supply voltage - see datasheet pg.12)
The various ways to do this would be to: either add a diode across the lower charging resistor, or add a second inverting transistor between the output and the TIP122. Or you could use a PNP transistor to drive your load.  

Diode option (ignore part number for NPN shown):



Simulation:



Or something like this:



Simulation: