whites changing color?!?!

hey guys,
i just got back from filming a buddy in his surfboard shaping studio and came across what i think is a problem w/ my gl2. we shot some white boards against a white wall and periodically changed the white boards out w/ a painted board (kind of a michel gondry effect) - anyways, i began to notice that the white wall which i white balanced and had looked really vibrant and white, would 'dissolve' to a yellow orange for a second and then back to white. it did this all night, for about an hour.
you should know we were filming under flourescent light in total manual mode with a flourescent filter


any ideas as to what this could be?

[Gints Klimanis]

I don't think your camera has a way to deal with the frequency differences between the flourescent light cycle and the shutter speed. I've observed similar oscillations, especially when vtaping under flourescent lights with shutter speeds at 1/180 and above.
My problems were reduced when I dropped that speed down to
1/60, but then my sports frame grabs were blurry.

[Don Palomaki]

Gints is correct. What you saw is likely a common artifact of using higher shutter speeds with discharge type lighting; e.g., flourescent lighting. Using 1/60 or 1/120 should be OK. The reasonis the the actual color balance of the light varies during the electrical cycle, and fast shutters only see part of a cycle. The part they see varies over time because frame rate is a bit slower then line frquency (in the USA).

wow what a great explanation gints and don! I am really happy to have learned that, although I wish i knew yesterday.
So 'discharge' lights are like flourescent lights... what other kind of lighting could give this problem?

[Don Palomaki]

The mercury and sodium vapor lights, often seen in parking lots and large buildings like warehouses and gyms may have a similar issue.

Note that some specialized lighting systems using flourescents may also use 3-phase power or high frequency ballasts that will tend to minimize this sort of effect.

[Tim Frank]

Would a flourescent filter prevent this all together so you could shoot at higher speeds, or would you still notice a difference?

[Don Palomaki]

Not likely it would fix it given that the filter is fixed - i.e., does not change its color. over time. It just would improve the 'average" accuracy of the color if you are using the color lamps for which the filter is intended.