Default Two Q's

Q1 Why do certain Roms drain battery faster? For example I get 5hrs sometimes 6 screen on time with CM 10.1 or 10.2. But on sense I be lucky to get 4hrs. What's eating the battery, why does the kernel eat it if that's what's causing it.

Q2 why does the camera on Cyanogenmod not take in as much light? It has this reddish purplish tent. While Sense Roms are clearer?

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