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I noticed that the cheap Chinese corn bulb that I bought were having insufficient DC filter capacitor. Change the value from 5uF to 33uF will reduce light flicker and prevent voltage spikes.
The filter over the CCD sensor is actually a polarizing filter. It let pass the reflected light (polarized) while blocking the direct light (non polarized). It improve contrast in high luminosity environment. An IR & anti-reflective coating is likely to be included on the front side of this filter