1 Jun 2011

Exercise: Tungsten and flourescent lighting

 Initially we are asked to participate in a few simple practical exercises.  Looking from natural light into a room lit with tungsten lights and then doing this in reverse.  So long as my eyes were accustomed to the initial light source I could definitely see the colour casts that would evident later in the photographs.  However, my brain quickly applied its own WB (White Balance) correction and whites soon lost their strange colours.
Looking at the light levels available in the room it was obvious that I couldn't hand hold the camera with the ISO set to 100 even with full aperture because the speed was down at around 1/4 sec.  In order to get a reasonable speed I cranked the ISO up to around 1250. 

The aim of the initial photographic part of this exercise was to demonstrate how the colouration of artificial light affects the camera and how to compensate for it.  We were asked to shoot an interior/exterior image where the light levels were balanced between both inside and outside and where the interior was lit by tungsten lights.  The images were to be shot at a variety of WB settings to demonstrate how WB changes the results.

 WB Tungsten

With the camera WB set to Tungsten the image has been corrected for the orange cast of the tungsten lamp so the colours in the left corner of the room around the lamp look natural but the daylight view and the light coming in from outside has a blue tint.  This is caused by the colour corrections the camera applies in the Tungsten WB setting.

WB Daylight

Now that the WB is set to Daylight the exterior view looks natural but the lamp and wall behind it has an orange/yellow cast produced by the uncorrected tungsten bulb.  It is impossible, in camera, to have a setting that can correct two different light source types at the same time.  This was an effect I used to my advantage when shooting this image for my Contrast assessment.

WB Auto

The WB Auto setting has repeated the temperature for natural sunlight giving a similar result as would be obtained for daylight.

Carrying on with the subject of colour casts from light sources the final part of this exercise required me to shoot images lit with fluorescent lights examining what difference can be seen between WB Auto and Fluorescent settings.

WB Auto
WB Auto

This images of Washington Metro and New York Train stations, shot with the WB set to Auto show a green cast from the neon lighting which makes the images look unnatural and unhealthy! 

WB Fluorescent
WB Fluorescent

With the Fluorescent settings the camera tries to compensate for the green cast and the colour returns to a more normal look.  Certainly, even with the corrections applied by the camera, the colour quality is poor as the lights do not emit the full colour spectrum.

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