ChAoS & PAIN: *... And On The Seventh Day, He Rested
"The idea that one should take an off week once per five weeks is one that arose as part of the Eastern European training methodology. The Eastern Europeans based their training on a centralized method, whereby they would take their athletes from their home for a month at a time, forcing them to train around the clock in state-run gyms, often fueled by sub-standard food and under stressful, prison-like conditions. As a result, the athletes required a full week of rest thereafter, when they would travel home, visit with their families, refuel and recharge, and then return to their around-the-clock training. Westerners never train under such ludicrous conditions, nor do they subject themselves to the volume of training that do Eastern Europeans."
Beyond that, I have no set training program and therefore I never plan light days. I go by how I feel every time I'm in the gym. I always push myself to to train hard and lift heavy.