artificial light foliage effects or virus ?

[sunset]

Hi

I would like you to have a look at the following photographs.

The blc had perfect green foliage before its culture under artificial light.

Under an intense artificial light (fluorescent), its foliage developed purple spots (photograph 1 – 2005 November).
Then, after November, I gave blc less light intensity and the spots are completely disappeared and foliage is beautiful (photograph 2 – January 28 - 2006).

In short, these spots are reversible and depend on light.

What can we think about that? I also thought it was virus spots but why is it reversible?.

Thanks, Philippe