should it be doing this??

hi all, im new to this an im not sure if i have a problem or not. Ive tried my light which is a brand new 600w growlux sodium bulb plugged in to a second hand digi ballest. I left it on for 20 to 30 mins and it kept going off and on not just flickering but just going off for liike 30 secs before turning its self back on again. Should it do this.

Doesn't sound right to me...

It is not. Could be a number of things, most likely it is your second-hand ballast causing it to flicker. The only problem I see it really having on your grow would be more wear and tear.