The main difference between the two is weight and folded frame length The Mutsy 4 Rider weights in at 23.2 lbs and the folded frame is 41 x 24.8 x 11.8. The Mutsy 4 Rider Light's weight is 19 lbs and the folded frame is 39.4 x 24.8 x 13.4. The rest of the specs are the same and as follows:

weight without wheels: 12.8
unfolded frame: 29.2 x 24.8 x 44.9
folded frame without wheels: 39.4 x 20.5 x 9.5

Hope this helps you!