1-2 seconds of very bright light outside, with no apparent source, shone through windows.

I did not see a craft, just a bright light.  We live outside of a mountain town in a dark area.  When up this morning at 4:30 MST, the whole sky seemed to light up and shone in the many windows on the open two-story south side of the house, illuminating window shapes across the floor.  It was so quick, 1-2 seconds of light, no apparent source but seemed to be shining slightly downward through the windows and the illuminated areas on the floor may have moved a little before all went dark again.  I looked around outside right after, didn't see anything out of the ordinary, did see a plane flying overhead on a usual path that we see planes up here.