I believe the DG XP95 are the lightest without an upcharge.  While you can also go with the Project X Pxi shafts with about a $35/shaft upcharge.   Also ... the Nippon shafts are very light as well.  

I have the XP95 shafts in my AP2 3 & 4 iron and Project X Pxi in the 5-PW .... love them!!  

As usual ... you should go get fitted for the best shaft for your swing.  There are so many good options out there.  Good luck! 

I have the XP95 shafts in my AP1 irons and I love them.  I hit everything the fitter had on the cart and picked this one.  They give me great ball flight and control on all my shots.  

I also tried various shafts in the AP2 and AP1 heads. As a 60 year old, I wanted more height and a naturally more distance and the X95 Regular gave me all that in the AP1's.

Had Project X 5.5 shafts on my old set of AP2s and when I got my 714 AP2s, they fitted me with the XP95 S300 shafts and when I stay in tempo, pure on target.   Great shafts...........