[taregg (OP)]

for light tube gas discharge

[taregg (OP)]

can you answer  quickly

[Bored chemist]

It depends
http://en.wikipedia.org/wiki/Paschen's_law

[taregg (OP)]

‏  can you explain depends of what.......

[CliffordK]

If you look at the graph from the Wikipedia that BC gave.



O₂ is not listed. 
However, compare the curves for N₂ and He.

The X axis of the graph shows a product of the (pressure * distance) separating the electrode plates.

For all higher pressures and wider gaps, Helium hits the bottom of the list.  I.E.  The lowest breakdown voltage.

However, there is a point with low pressures and narrow gaps, that Helium performs better than most other gases, except for Hydrogen.

[taregg (OP)]

what makes elements of gases low or high  break down voltage from same of atom structure...

[CliffordK]

BC will have to give a better answer.

It appears as if the chart on the left side is dominated by atomic/molecular size.

On the right, it appears to be dominated more by electronegative, and "free" electrons, but I would need more data to confirm.  Surprisingly the Helium which is one of the least electronegative elements is at the bottom of the graph.

I would be curious about more gases, chlorine, fluorine, oxygen, methane, and etc.