When taking pictures of subjects that are illuminated with fluorescent light
using a digital camera it is possible that
variations in white balance from image to image can occur.
As a result, the overall colour cast of the photograph can change depending on the exact
instant that the shutter
is released even thought the lighting conditions are constant..The reason for this phenomenon is that the colour temperature
of the light source changes during the power cycle.
For normal AC lighting systems, the power goes from full to zero 100 times per second
according to the variation in voltage.
- Incandescent lighting has a high thermal capacity (the filament
remains hot) so the temperature
and colour remain relatively constant.
- Fluorescent lighting however uses a different method of
illumination and the colour will change from
instant to instant.
Our eyes do not detect this change as it happens too fast for
us to recognise.
However, the camera is able to capture an instant in time that the eye cannot, and when a
picture is taken with a fast shutter speed
these variations become noticeable.
The phenomenon therefore occurs when the shutter speed is
comparatively faster than the frequency of the AC power source to the light.
The examples below shows eight exposures of a neutral grey card
taken with a Nikon D-1 at 1/320th second and f1.4.
The swatches on the left were with shot under normal 50Hz lighting, and those on the right
with high frequency lighting.
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