The thing that I found particularly interesting about my cardio experiment is that I'm already more fit and active than average. Every other day (barring the occasional extra rest day), I'm at the gym, doing 60 - 90 minutes of free weights. My heart rate is often 140 - 170 when I come off a set, and I pretty much jump on the next set when my heart rate hits 125. By the definitions I found, that is technically cardio, yet doing 30 minutes of daily bike riding still seemed to have an effect.
I've also found that having a bright light helps, particularly in the darkest of the Pacific Northwest winter months.
I started taking 2,000iu of vitamin D upon waking, too. This may or may not help with wakefulness and may or may not assist in combating depression.
An experienced running coach has recently opined that spending an hour in the gym doing strength is about equivalent to 10 minutes of running.
Part of the reasoning could be the activation of different energy systems. Lifting activates the anaerobic system, whereas sustained cardio activates the aerobic system and dips into the anaerobic only at higher levels of effort. The anaerobic system transmits something like 30+ ATP (energy currency of the body), whereas aerobic is 2 ATP [1]. That might explain why you experience this difference.
I've also found that having a bright light helps, particularly in the darkest of the Pacific Northwest winter months.
I started taking 2,000iu of vitamin D upon waking, too. This may or may not help with wakefulness and may or may not assist in combating depression.