Can you read the bulb for me?
I assume since your outdoor its probably a Mercury ( more liekly today metal halide but same basic ballast ) or High presure Sodium.
If its white it the first, a light yellow tint High presure Sodium dark yellow with no colour then low presure Sodium.
Your best option is to replace the starter if you can, some have it built in and you need to replace it.
If the light ballast is B/O you may be better off to replace the entire unit, I'm found of the low presure Sodium. For outdoor use I find the SOX 55 is the cheapest most reliable you can buy. No starter to fail, more light per watt and they guve clear warning they have reached the end of life by turning pink.
When any HID light starts to flick on and off its a warning the bulb is done. Replace it ASAP or the balllast and or starter will start to fail from trying to start it over and over again.
Metal Halide is probably the nicest clear white light you can buy if the colour spectrum is important low presure Sodium is the worst. high presure is a comprimise between the two....