Reducing GO with Flash light !??

Although the use of camera lash has been reported in CNT, Si nanowire and conducting polymer. This work still gave me a big shock.
http://pubs.acs.org/doi/abs/10.1021/ja902348k

Researchers from Northwestern University (the alma mater of my master adviser) had invented a new way to reduce graphite oxide. They used the commercial camera's flash light to irradiate the GOs and make them back to graphite and accounted for this effect by using photothermal heating mechanism. They found that the flash method is effective enough to compare with themal annealed samples. The basic principle is about the water evaporation from the GO, and the enough photo energy to trigger the deoxygenating process.

Taking advantage of flash light, they even make a photomask to define the device region. This is a very useful method for GO approach, and they demonstrated again that the camera flash is able to be a tool for reduction proecess.

I just wondering why the flash light irradiation in ambient condition could be a reducing agent for GO while being a oxide agent in other cases. @_@