The brilliant flash of light can burn out the retinas of the eyes if looked at. The thermal pulses can burn flesh and set flammables on fire. Thus, if you see a brilliant flash of light — maybe 25 miles away, immediately turn away from it.
White clothes reflect light and this can protect and/or reduce flash burns where thermal radiation is a hazard. As a crisis worsens, and you work outdoors, wear white shirts and pants, hat and gloves. Or have the gloves on your person to quickly retrieve and put on as you dart for cover.
The intense flash and thermal radiation is of such intensity, if one is next to a concrete wall or some other rivetment, as shown in the video of Hiroshima, as they are instantly vaporized, the speed of light burns their shadow into the wall.
Interesting piece, a friend told me about wearing white in a nuclear explosion but... yeah nice find. Might help you survive one. :P
Read it all here:
http://www.ih2000.net/chembio/nuclearblastsurvive1.html