ill post here instead on the pm panther.
the idea of incorporating a light and heavy day is fine, however you have to have a split which allows time to still recover before hitting similar areas once more. four out of five days training wont allow this and usually, a light/heavy split is used when targeting a weak point (example: if someone is trying to up their chest, they might consider having a light day, where the total sets as well as the weight being used are less than your norm) but to have a heavy and light day for all body part, adequete recover will be hard to come by. heres what i would do with your M-Tu-Th-F split, keeping the light/heavy technique but for one body part (i will use chest, you can change that if some other area is a weak link), but changing up the muslces trained per day.
Monday (heavy chest w/ tris and shoulders)
bench 3 x10,8,6
dips 3 x failure (this is fine, however add weight if failure is coming pass 10 reps)
db or bb incline chest press 3 x 8,8,6
fly 2x 10 (thats fine)
shoulder press 3 x 10,8,8
close grip 3 x 10,8,8
skulls 2 x 10 (total of 19 sets for chest/shoulders/tris)
Tuesday: (legs)
squats 4 x 12,10,8,6
SLDL: 3 x 10
front squats or extentions: 3-4 x 10,10,8, (8)
leg curls (perferably lying): 3 x 10
lunges (walking is fine): 2 x 10 (4 sets, esp if the distance you travel is a good length, is a lot)
Thursday: (Back/traps/biceps)
chins 3 x failure (again, like the dips, add weight if you fail after 10 reps)
pulldown (use various attachments to hit different areas): 3 x 10,8,8
Deadlift (rack/partial): 3-4 sets x 10,8,6,(5)
bb/low(i assume you talking from the cables, db): 3 x 10 (fine)
bb curls: 3 x 10,8,6
incline db curls: 3 x 10,10,8
(another bi exercise optional)
db/hammerstrength/bb/reverse shurgs: 4 x 10,10,8,8
Friday: (light chest, shoulders,abs, calves, cardio if you dont do so already)
military bb shoulders: 3-4 x 10,8,8,(6)
arnolds: 3 x 8
side laterals: 3 x 10
flat/decline/or incline bench: 3 x 10 (use 60-65% or so of max)
whatever abs you do. (of course, you can tran abs the days you lift as well)
standing calf raise: 4 x 10 (could also move this to tuesday
Sage