Interesting CYA observation

[Randrx2]

I have been mostly testing my CYA indoors and get expected results for my light conditions. I have the 50 ppm calibration standard so I know what a disappeared dot looks like for my conditions.

Today I did an indoor test and then took it outside to compare. What was interesting is that the results were about the same with the sun at my back in the morning. However when I went to the covered part of the patio in the shade, I could see the dot (with same amount of water on vial).

I would have expected a test in three shade to give a higher reading since it is “darker”.

Is there any science to this phenomenon?

 

[JoyfulNoise]

Yes. It’s called nephlometry and it’s the science of light scattering from suspended solids or turbidity. Your eyes are very sensitive optical imaging organs. They can distinguish patterns and details based not only on color but also shade and grey scale. When you increase the amount of light entering into the view tube, the amount of light scattered up to your eyeball increases. This extra light can overwhelm some of the sensory structures in your retina effectively “washing out” the image. In lower lighting conditions, your eye can more easily distinguish edges and transitions.

The CYA test is designed to produce correct results when the tube receives oblique lighting (which is why you should hold it so that your hands don’t obstruct the tube) and tube is roughy 2 ft or so from your eye. Indoor lighting usually isn’t bright enough for most people but if you are getting good results with your standard then that’s fine.

 

[Donldson]

Real world example: driving through fog. I'm sure we've all been told (whether we do it or not) to use the low beams in fog, even at night. That would be why.

 

[Randrx2]

Yes. It’s called nephlometry and it’s the science of light scattering from suspended solids or turbidity. Your eyes are very sensitive optical imaging organs. They can distinguish patterns and details based not only on color but also shade and grey scale. When you increase the amount of light entering into the view tube, the amount of light scattered up to your eyeball increases. This extra light can overwhelm some of the sensory structures in your retina effectively “washing out” the image. In lower lighting conditions, your eye can more easily distinguish edges and transitions.

The CYA test is designed to produce correct results when the tube receives oblique lighting (which is why you should hold it so that your hands don’t obstruct the tube) and tube is roughy 2 ft or so from your eye. Indoor lighting usually isn’t bright enough for most people but if you are getting good results with your standard then that’s fine.

Thanks Joyful!