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Superluminal light pulses
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Photons and other particles cannot travel faster than with 
velocity c, the vacuum speed of light.

However, light can appear to move faster than c.
The reason is that there are different kinds of velocity, behaving 
differently. The group velocity of light can (in a medium) exceed c. 
But the information velocity (or signal velocity) is always bounded 
by c. 

One cannot attribute the group velocity of alight pulses to a photon
in the technical sense of the word (as a single excitation of the 
electromagnetic field) but only to the light beam as a whole.

For more details, see the Wikipedia article
     http://en.wikipedia.org/wiki/Group_velocity
''However, in all these cases, photons continue to propagate at the 
expected speed of light in the medium.''