Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: verycuriousguy on 15/01/2019 23:38:48

Title: Why is flat light made better if there are trees around?
Post by: verycuriousguy on 15/01/2019 23:38:48
Sometimes, in skiing, there is flat light, when clouds completely cover the sky.  In flat light, it is very hard to see surface features, e.g. small features or curves in snow.

Yet if you ski near the trees, visibility is much improved.

Why is this?  Doesn't seem like it could be about shade.
Title: Re: Optics/visibility question
Post by: chris on 15/01/2019 23:49:41
Lovely question, but can you please edit the thread title to format it as a question, in line with forum policy? Otherwise the thread will be deleted. Thanks.
Title: Re: Optics/visibility question
Post by: Bogie_smiles on 16/01/2019 00:09:39
The optics of the flat light that you refer to are the monotony of the snowscape and the lack of any features that stand out. Add the presence of tree trunks and the monotony is broken, and you have something that allows you to gage the scale of differences in the shading of the snowscape, don't you think?
Title: Re: Optics/visibility question
Post by: verycuriousguy on 16/01/2019 00:28:49
I had no idea as to the cause, not even a guess. but your response sounds plausible. 

The flat light situation I'm talking about is quite look down and you can see your feet, but if you're not around trees you really have difficulty seeing the surface.
Title: Re: Optics/visibility question
Post by: evan_au on 16/01/2019 00:34:23
Our eyes detect the edges of objects by changes in color and brightness.
- Snow is a uniform color
- When there is an overcast sky, lighting is uniform, there are no shadows, and there is little variation in brightness

If we are close enough to objects (15 feet or 5 meters), our eyes can pick out additional cues due to binocular vision - but you need some variation in color, brightness or texture to allow your eyes to "converge" properly.

However, if you are near trees, that provides:
- A strong difference in color
- A shadowing effect, so that objects are no longer uniformly illuminated
- Some clear edges to assist convergence