 Poster: A snowHead
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Obviously going around in circles on this one.
The key points are that flat light is simply a low contrast situation and is usually caused by overcast conditions i.e. diffuse lighting - no shadows. It is that simple. When the sun pops out, shadows appear and the flat light is no more.
A white-out (in skiing terms) on the other hand is a severe lack of visibility usually a result of being immersed in low level cloud (fog). But could also be caused by heavy snow conditions. You literally can't see more than a few feet ahead. Everything basically looks white and you can't tell snow from sky.
Wayne, your physics definitions of the above are really not cutting it for me, especially your flat light definition. It just seems like you've applied completely the wrong physics to what most people would perceive as flat light.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| Quote: |
while fog reduces visibility, for me, in a ski context 'White Out' would be about snow\blizzard
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when a French weather forecast warns of a "jour blanc", I think this generally means cloud and therefore very little visibility, rather than a blizzard.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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pam w, pah, what do they know. In England Snow is White, Fog is Grey 
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| meh wrote: |
Wayne, fair enough although that isn't really a definition of flat-light/white-out but the conditions that lead to flat-light/white-out, amended:
Flat-light: Lack of visible definition in the snow surface caused by diffusion of light, often by high cloud. (just for reference I've seen it in ash cloud as well after the Grimsvotn eruption last year, although it's less obvious without the uniform coloured surface)
White-out: Lack of any visible definition caused by diffusion of light and reduced visibility, often by cloud at ground level. (although you can be in a white out with pretty good visibility and high cloud as long as there isn't anything to provide contrast, as per the photo on the wiki) |
Just joined thread and haven't read beyond this quote so far-
But wanted to jump in:
White out to me means that light travelling towards your eyes is absorbed / scattered / whatever reducing visibility
Flat light to me really is to do with REFLECTED light, in skiing this means off the snow. With overcast skies causing flat light incident light rays are scattered thus so are reflected rays. Your eyes and brain perceive distance / 3D etc by variations in the reflected rays, so anything that affects these will affect your perception of distance, majorly if everything is the same colour and there are no shadows either to give clues to your brain
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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This is particularly a problem with moguls. Your eyes / brain are getting inputs from scattered reflected rays, and if not sunny no shadows to give cues to your brain. This is further aggravated if no trees around to give cues re fall line
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| Wayne wrote: |
uktrailmonster,
Yep, you may be right.
I have gone along the lines that anything (fog, cloud, falling snow, spindrift, some types of rain, etc) that will scatter the spectrum (basically so we see white) will cause a white-out.
Most of the pictures I see of cloudy days that are shown as flat-light I would say are really white out.
Just trying to keep them separate (the conditions) not the effects and these are sometimes quite similar
You can have flat light on a sunny day but not a white out (below the dew point)
For flat light I have gone with the increase in color (normally around 430nm to around 500nm / blue end of the spectrum) due to a vast number of small particles being present at the right size to reflect small wavelengths. The basics being that this will sort of - but not quite - form a Reighley effect but with a particulate base |
I am not sure about flat light on sunny day, unless the sun is very low in sky and you are in shade
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| Wayne wrote: |
| clarky999 wrote: |
| Have to say I like meh's description a lot better. |
But diffused light is, by definition, a white-out
Flat light is (may be wrong about this) light that cause objects to appear flat and uniform and without discernible features |
Yes, the reason because the reflected rays are scattered so confusing your eyes/brain, coupled with absence of cues due to shadows, colour etc
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You'll get to see more forums and be part of the best ski club on the net.
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In a proper white-out you wouldn't know (or care) whether there was "flat light" because you wouldn't be able to see the ground ahead anyway.
What IS interesting is why on some dull, cloudy, days you get very flat light, and on others, which seem equally dull, you can see the contrast/shapes on the ground much better (I agree colour is irrelevant). Only a minority of cloudy days also have proper flat light, I'd say, the sort when you can see neither a mogul nor a big ditch.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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altis, those are great picture examples. Every piste map uses same trick. Our brains rely on cues like shadows, relative movement etc, when the reflected rays coming to each eye are not sharp.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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pam w, this is definitely true. Maybe wayne could explain why
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| abc wrote: |
Wayne, I think on the flat light bits, there's a pretty big difference in what you define and what the rest of us think.
For most of us, flat light has nothing to do with color!
Reading through most of the posts, that's the impression I got. Flat light is purely and simply due to too many light sources from all directions. So all shadows are washed out. And one can't see the moguls or even the surface sloping down vs up. But one can still see quite clearly a lift tower, or the piste marking post from a good distance away.
In the white out, one may not be able to see even the piste marker till one's almost right in front of it. |
Sorry for posting so much before finishing reading whole thread. If I had seen this sooner cudda just done +1.
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You know it makes sense.
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For me, a white out is a lack of visibility because the air in front of you is filled with white stuff (snow/fog), whereas flat light is lack of contrast. I think all 3 of Meh's photos earlier in the thread show flat light - the only difference is that the rocks in the 3rd one give some contrast, but if you were to ignore them, conditions are very similar to those in the other photos.
An easy way to tell the difference - in a white out you can't see your skis.
And another one - in flat light another skier or a tree helps (provides contrast), whereas in a white out you can't see the other skier or the tree.
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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As usual abc talks sense.
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Poster: A snowHead
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In climbing terminology a white out is when there is no definition between the ground, the horizon and the sky. All merge. Anything else is flat light and difficult conditions. When you are in a white out the perception is that of being inside a ping pong ball. Plenty of studies published on this.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Tom Doc, believe me in the first two photos the visibility is no more than ten meters.
This is how the vis was about half an hour previous and we skied from the pinnacle which is actually still several hundred meters away in this photo at the site we couldn't see it at all except for the occasional slight break in the cloud:
http://i.imgur.com/K7U9F.jpg
Just illustrate further check the icing on pretty much everything I'm wearing before skiing down, not just poor light there but sitting in a cloud:
http://i.imgur.com/l80Rh.jpg
I think not being able to see you skis is a bit excessive, who would actually ski in such conditions as it implies you cannot see more than two feet? What Scarpa said is the generally accepted idea of what a white out is.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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You need to Login to know who's really who.
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OK looks like that may still be the US meteorological definition but the Met Office states this on their mountain forecast background pages:
| Quote: |
| White-out conditions are defined as when one's field of view becomes totally featureless due to a combination of mist or fog and deep snow cover, with or without falling snow. |
Criteria requires snow, but necessarily falling or drifting.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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I might not be right, but if its any help this is how I view things:
I tend to think of flat light per se as being un-connected with precipitation in the air or with being inside a cloud - instead I think it is caused just by wierd light on the snow which might be caused by combinations of higher cloud that you aren't actually skiing through affecting how the light hits the ground - it is the sort of light that removes all definition from the surface and in a completely covered snowy area is sufficient to remove the contrast that would otherwise show undulations, the edge of the piste, moguls etc.
IMO white outs are everything else and themselves result in a lack of contrast similar to flat light, It needn't be snowing heavily, you could just be skiing inside a cloud with no apparent actual preciptiation occurring, but the lack of vision is caused by the water droplets in the air hence it being linked to precipiation effects if precipitation is condensed water vapour in the surrounding air of some form. I've seen white out conditions take vis down to less than half a piste markers distance and to a point where you can't see what you are skiing on.
All I know is that I hate both conditions - if you are on the wrong piste they can be dowright dangerous - I was amazed to get down the col de l'audzin in VT in one piece!!
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Whiteout: vision obscured by falling snow
Flat light: light so diffused contrast is vastly reduced
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Winterhighland, yes a white out needs lying snow otherwise the reflective properties of the surface are not sufficient to cause the disorientation. The contrast difference between the ground and the cloud in the air needs to be very low. For example here in the ash cloud last year the disorientation was nowhere near as bad as it is when it is snowy with the differing reflectiveness of the ground.
The Met Office definition is exactly the same as mine. Featureless due to cloud and/or snowfall with snow on the ground as per my photos and your own. Flat light is a similar condition but where the definition of the snow surface is unintelligible.
Megamum is dead on.
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*****************************
As I said above, I may have cocked up in what I consider White-Out & Flat-Light to be compared with the common perception.
So I am re-looking at it and will re-do it, obviously if the majority of people consider a condition to be termed is a certain way, then that’s what it is (normally).
I think I may have been discussing something that wasn’t what is commonly known as “flat-light”.
e.g. we all know what a spade is don’t we. OK there are lots of different types of spade, but in general, when we use the word spade it brings to mind a certain type of thing. It doesn’t, for example bring to mind a fork. So the term used to describe something is what matters here.
But the cause for the condition, which everyone describes as Flat-Light may not agree with the common perception. As I said I’ll re-look at this.
Having said this, I may get it wrong again and, in this case, I have every confidence that you tell me  .
Note – if I didn’t want you to tell me when I was wrong, then I wouldn’t have asked (I have plenty of student that will agree with everything I say) – so thanks for all the feedback.
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You'll get to see more forums and be part of the best ski club on the net.
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I think the thing with what I call flat light is that theorectically you can still see some considerable distance ahead through the air - you just can't tell that you are looking across any distance! - you could still see someone 30 yards away from you, you can't see the definition of the surface you are skiing on or that around you for ANY distance. When you have precipitation in the air (what I call a white out) it is the physical prescence of the precipitation be it snow, water droplets (the skiing inside the cloud scenario), fog etc. in the air which prevents you from seeing, though it may of course also result in the light flattening.
I skied in plenty of conditions like both of these in Feb and April. What I found was that the fog/cloud was marginally easier to ski in as it tended to not always flatten the light per se, in many foggy conditions you could distinguish the snow texture about 2m in front of you where as in flat light you most certainly can't. Hence why I wrote above 'May'. It is possible to have fog/snow without flat light (IME more often than not the light was not so flat with precipitation causing the lack of visibility), and flat light without any form of precipitation (that's when it really does my head in).
My worst experience in VT was the col de L'audzin in April skiing in a cloud - white out conditions, in Feb we got flat light (no precipitation) up above Zauchensee (Austria) which was really dire - of the two I think Austria was the worst (but there wasn't much in it - I nearly panicked on both occasions).
I love skiing on bluebird days best 
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Megamum, you can see as far in flat light as in 'clear' conditions. Flat light simply refers to clear conditions where definition is reduced by some phenomenon (other than obscuring) to the point where similarly coloured topographical features (eg moguls) disappear, so the piste looks, well, flat really.
A white out is caused by mist, snow, low cloud etc obscuring the vision to the point that horizon lines and other reference points are removed sufficient for disorientation.
You've been bang on with what you've been saying. (to my mind anyway)
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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| Wayne wrote: |
| I think we are (maybe) straying away from a definition of condidtion and causation and getting closer to a description of the results. |
Wayne, I bet to differ. I believe part of the disagreement is indeed what 'result' you were trying to define.
Before we can move on to the causation, we must first agree on the effect: description of the result.
Otherwise, we'll be forever argueing about the definition of 2 different phenomenon, which can not possibly be the same.
As a teaching assistant long times ago, one of the most common protect from student about their grade was their answer was correct, to a question that was NOT on the exam!
However, in one rare occasion, the student pervailed because he was able to convinced the prof the question itself was ambiguious!
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You know it makes sense.
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OK then - 2nd stab at it.
Comments 
Flat-Light is caused by a Diffusion of sunlight.
Due to the presence of airborne reflectors such as ice crystals and water molecules, plus ground lying snow, light is reflected from all directions.
Result
The scattering of light in all directions removes indicators such as shadows and tones making it difficult to discern similarly coloured slope features such as depressions, moguls and other gradient changes. The loss of visual indicators of shape and edge detail results in objects seeming to blend into each other, producing a Flat featureless vista. A bi-effect of visual blending is a loss of depth of field resulting in disorientation.
A white-Out is caused by a Reduction in (and the Scattered Reflection of) sunlight.
Reflected light from terrain features is physically blocked e.g. by falling snow, low lying clouds, localised fog, wind-blown spindrift, etc. resulting in a reduction of visual references; the light Reflected from the airborne particles is Scattered and blended into white.
Result
The Blocking of visual reference points such as the horizon, terrain features, objects, gradient, slope aspect, etc. may result in an inability to discern movement and a loss of balance; a loss of proprioception is commonly reported. A White-Out leads to an overall reduction in an ability to operate within the area, due to a lack of reference points, and the increased danger (actual and perceived) this presents.
Last edited by You know it makes sense. on Mon 14-05-12 11:10; edited 1 time in total
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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Wayne,
I still think that the word contrast should be used somewhere. Contrast is a simple concept and is widely used in descriptions of the effects on the discernment of features (e.g. the ability to discern structures and pathology in radiology is referenced to the ability to achieve suitable contrast. Sorry to bang on about it but that's how I feel. Insert the word contrast after the word tones in the definition of flat-light.
I often find in white out conditions that it is difficult to discern the direction of movement as opposed to just movement
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Poster: A snowHead
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Having always suffered from nausea dizziness and balance problems in poor light skiing, I went to the Uvex colour lab that checked me out and found I had sensitivity to grey, lens to take out grey light worked absolute wonders made John Major almost acceptable...
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Some people DO have difficulties with certain colours which can cause problems, for example, with pereception while reading. For sufferers, text can appear to 'swim' when printed on white paper. The solution is to use different coloured paper or wear tinted specs. I imagine that similar problems can occur while skiing where, essentially, the 'page' is white.
Check out Irlen Syndrome.
http://en.wikipedia.org/wiki/Scotopic_sensitivity_syndrome
Apparently, different sufferers require different coloured specs (or paper). Perhaps this is the reason that different people get on better with different coloured lenses when skiing in flat light.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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Wayne, I think the new definition is much simplier and clear than before.
One minor quible:
| Quote: |
A white-Out is caused by a Reduction in (and the Scattered Reflection of) sunlight.
Reflected light from terrain features is physically blocked e.g. by low lying clouds, localised fog, wind-blown spin-drift, etc. resulting in a reduction of visual references; the light Reflected from the airborne particles is Scattered and blended into white. |
Shouldn't the part following "resulting" go into the "Result" section?
This should simplify the definitions and clarify their difference: White out is light blocked, and flat light is light diffused.
The finer consideration of physics: flat light concern more about the source of light, while white out is due to reflected light unable to reach the eye.
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You need to Login to know who's really who.
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Wayne, Massive improvement over your first attempt! I can now relate to both these descriptions. As halfhand, suggests I would also use the term "low contrast" somewhere in your flat light description. It's the first word that comes to mind when thinking about flat light.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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| abc wrote: |
| The finer consideration of physics: flat light concern more about the source of light, while white out is due to reflected light unable to reach the eye. |
Hmmmm, not really, as this would suppose that a white out is perceptual (visual illusion), but it's not. Even if there is no eye there to receive the light, the condition would still exist.
******************
Right it’s done, well I'm sticking with this - of course things can always be improved (e.g. I took out the reference to proprioception and used kinesthesia instead) - there are no doubt other sections that could be improved, but no time right now.
 This isn’t even part of the work; it’s just one of the reference notes at the back. I did look all over Google for this but couldn't find one that I agreed with, hense doing my own - that you may or may not agree with.
Thanks for the feedback. Best get on with the rest now.
Flat-Light is caused by a Diffusion of sunlight.
• Cause
Due to the presence of airborne reflectors such as ice crystals and water molecules, plus ground lying snow, light is reflected from all directions.
• Result
The scattering of light in all directions removes indicators such as shadows, tones and contrast making it difficult to discern similarly coloured slope features such as depressions, moguls and other gradient changes. The loss of visual indicators of shape and edge detail results in objects seeming to blend into each other, producing a Flat featureless vista. A bi-effect of visual blending is a loss of depth of field resulting in disorientation.
A white-Out is caused by a Reduction in (and the Scattered Reflection of) sunlight.
• Cause
Reflected light from terrain features is physically blocked e.g. by low lying clouds, localised fog, wind-blown spin-drift, etc. The light Reflected from the airborne particles is Scattered and blended into white.
• Result
Visual reference points such as the horizon, terrain features, objects, gradient, slope aspect, etc. are significantly reduced or blocked, leading to an inability to position yourself relative to the surroundings. In severe conditions, due to a loss of kinesthesia (ability to discern movement) confusion, loss of balance and occasionally nausea, has been reported. A White-Out leads to an overall reduction in an ability to operate within the area, due to a lack of reference points, and the increased danger (actual and perceived) this presents.
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You'll need to Register first of course.
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Yes, a definite improvement, particularly for the flat-light definition which is what I had problems with before. As a photographer I'd be using phrases like hard directional light (such as full sun) vs soft ambient light (such as complete cloud cover) with the latter resulting in the flat light conditions with no shadows. But the physics approach is just as valid (if not more so) I'm sure.
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Wayne, looks good to me.
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A picture is worth a thousand words:
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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altis,
Your sun doesn't look as happy as my daughter's.
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FAQ
as does 
. Keep in mind that whatever I come up with is only my idea and every single person who has ever been skiing will have their own ideas which are just as likely to be correct. But I promised to mail a reply to all the enquiries.
