Hi Zhe and Raquel,
my thought on this below...
Best regards
Axel
On 01/03/17 18:27, Raquel Viula wrote:
Hi Zhe,
3) Does lighting source influence the accuracy of the factor? Focusing
on daylighting data collection, should I take images under consistent
electric lighting conditions or daylighting conditions? (Daylighting
conditions have dynamic changes, but electric situations offer lower
results.)
Different light sources will provide different calibration factors. I
was told by the seller of my system that a measurement under white LED
has errors of 5 to 12% in relation to the measurement done with a
halogen-based calibrated camera. But LED has a lot of flicker, doesn’t
it?
I looked into flicker some time ago, and presented my conclusions in a
presentation at the 2012 Radiance workshop:
http://www.jaloxa.eu/mirrors/radiance_workshops/2012/Talks/Jacobs-AJ09-HDR_Radiance_WS-2012.pdf
Skip to page 23 for flicker.
In short: If you are seeing the actual artificial light sources in the
photograph, then you need to use short exposure times to capture them
accurately. In this case, it is safe to assume that the lights flicker
(simply because most do, particularly LEDs), and are not accurately
represented in the HDR. If HDR glare measurement is what you want to
do, this is obviously a problem.
You probably won't have the equipment to measure flicker. What you can
do is take 5 to 10 photographs with the shortest exposure time you need
for your sequence. Keep all camera settings the same. If all
photographs look identical in their brightness, the light source is
flicker free, or flickers at such high frequency or with such a low
amplitude that you can ignore it.
Hope this helps
Best
Axel
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