If you're lifting for hypertrophy, more reps is better than more weight, e.g. 15 reps of 100 lbs instead of 6 of 150 lbs or whatever your maximums may be.
Physical education students were matched into three groups; G90 (n = 9) trained with a load of 90%, G35 (n = 11) with 35%, and G15 (n = 10) with 15% of 1RM (1 repetition maximum). Training consisted of three to five sets, performed three times a week for 9 weeks. Each set consisted of two, seven and ten repetitions in G90, G35 and G15, respectively. Training was performed with the nondominant arm, and the dominant arm served as control. The 1RM increased 15.2 (SD 4.5)% (P < 0.001) in G90, 10.1 (SD 5.9)% (P < 0.001) in G35 and 6.6 (SD 7.9)% (P < 0.05) in G15.
This bit was surprising to me:
In the untrained arm, 1RM also increased for G90 and G15. In contrast to G90, G15 showed a similar increase in 1RM in both arms.