Hi everyone i was just wondering if i switched on my fluorescent light what would happen if i place my plasma ball near it would the light go off ive lit the tube up when its been switched off just wanted to know what would happen if the light was swiched on 

I think nothing at all. Maybe some change in brightness in the area where they touch

The current in the lamp is hundreds mA (tens mA in small ones). The current from the plasma ball is oreders of magnitude less

I understand what "slayersdeath" want to ask: If a plasma ball would do things to an operating fluorescent lamp.
Plasma ball don't affects lit lamps, only unlit ones.
When touching a plasma ball on a fluorescent lamp, the area of the lamp near the plasma the plasma starts to glow dimly. When the lamp operating, the power of the electricity field of the plasma ball is too low to cause the lamp to change brightness, however trying to do this with an EOL lamp may cause them to get back to life (More effective with fluorescent nightlights (Which are sufficient small and haven't any EOL shut down protection as most CFLs), and HID lamps).
I used my plasma ball to check the color of my Hyundai TEVA amalgam CFL lamp when it is cold, to confirm finally, that unlike how they are advertised (Liquid mercury free and Amalgam), they contains liquid mercury and vapours as well and so that every advertisement that states a specific CFL as being liquid mercury free is false and misleading.
Here is my picture of this confirmation.

You can use the small piezoelectric element from a lighter to light up fluorescents / incandescents* / HID** in short pulses

* try it. the gas filling will  break down and you'll see "lightnings" inside

** if you try to strike a MV when touching the lamp from outside, the phosphor will break down with red "lightnings" across it

The plasma ball (or better to say it's Tesla transformer output) is more reliable - it is able to hold the ionization for longer time and in larger volume then tiny sparks, so it is way more likely to transition to thick, fat arc.

I tryed to light up my 160W SBMV lamp in my room at my father home (Which is elliptical) by my plasma ball, but the lamp didn't glowed.
In contrast, a member in LG, succeeded to ignite a tubular MH lamp, with his plasma ball, without the need of an ignitor.
Why is this? Is this related to the distance between the plasma ball and the arctube that the shape of the outerbulb of the lamp dictates?

You need to create sufficient voltage across the arc tube (from electrode to electrode, or form capacitance of outside objects to an electrode)

With the SBMV, maybe the arc tube was too far away, or maybe it was "blocked" from the plasma globe by objects at earth potential (frame, filament. . . ) so that too little potential difference was between any 2 points in the arc tube

With the MH, meybe the frame was "floating" and the other electrode at earth. The plasma globe set high potential to the frame, and there was sufficient potential difference between it and the opposite electrode of the arc tube. Or both electrodes were at earth potential, but he managed to make high enough potential in any point in the arc tube, only by capacitance between the globe and the arc tube (If so, perhaps he would not succeed if he did it from the side where the frame / flywire would block the way)

Other factors : Different output of different globes, different arc tubes (in size, starting gas fill, proximity to outer glass), lamp being screwed into light fixture (which is equal to connecting both connections to earth) etc

MH: If te MH contain framing, it is most likely not connected to anything (to allow positive potential to build up there, so repel sodium ions from arctube wall), so it then create brdge to carry the HF current towards the arctube, so the HF current may flow from this frame to electrodes. Depend, how you hold it, either the frame is more grounded and electrodes are live (holding the bulb, approaching the plasma ball with the socket) or main electrodes are grounded and the frame is live (holding the socket, approaching the ball by the bulb), in both cases you have current to light up the gas in the arctube.

230V SBMV: Mercury lamps have starting resistor and probe, what create parallel path for low current, but with low breakdown voltage. So it may easily happen, then the discharge build up only from the auxiliary probe and this then clamped the voltage, so prevent it's buildup between main electrodes.

120V SBMV: These lamps have in cold state the discharge tube effectively shorted (they are in the "preheat" configuration), so you can not build any significant voltage between electrodes.

My SBMV lamps are Osram HWL and Philips ML. They only have an argon negative glow around the first and the third electrodes when i tough the base of the lamp with my plasma ball.
I think that they have also a frame wire.