Oswald, bright lights, and the sixth floor.

[Chris Bristow]

At the time of the shooting the Sun's elevation was 37 deg and the azimuth was 8 deg.
Around frame 130 the Sun's azimuth would line up with the trunk or hood of the limo and the corner of the TSB. (I'm taking the slope of Elm into account.) Bouncing off the trunk at 37 deg the reflection would land on the TSB 66 ft above the trunk of the limo. That is approx 3 ft from Oswald's eye level. I know everyone uses slightly different figures for Oswald's elevation but I think a reflection traveling that far would expand and be may ten or more feet across. The fact the limo trunk is curved means the reflection would have to spread out to the side.
 I think it is likely whoever was in the window experienced a moment of glare off the hood and trunk as they were about to fire at 133. I don't know if it would have been blinding but if he was looking through the scope at that moment and caught a bit of the trunk that would be very bright, imo.