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Re: ski slope lighting

Sorry for the delay in my response. It has been an extremely busy month, and I
am just now getting to my "fun" emails.

You are very correct in limiting the brightness to 1 cd/m2. We have run
experiments on ski slope lighting and have produced lighting to about 3 times
full moonlight, or around 0.3 lux. In Colorado, people readily ski under full
moonlight, and so we tried to duplicate these results. The key to great ski
slope lighting is not the amount of light, but how you light it. High amounts
of "flat" lighting similar to a cloudy day can result in disastrous skiing
conditions. But, if the lighting highlights the terrain roughness with
shadows, skiers can easily see even under low lighting conditions.

Our experiment involved many expert skiers, skiing at high speeds. We asked
them when the lighting was too low for them to feel safe. It was below 0.3
lux. We also employed a vision scientist, and he said that there was plenty of
light to ski and that we could even go lower.

So, the important thing, is to install uni-directional lighting. Do not aim
the lights uphill at all. With lighting that is "full cut-off" asymmetrical
luminaires, aimed downhill, and the lens parallel with the slope, you should
have great results.
Good luck,
Nancy Clanton

Jan Hollan wrote:

> Dear Nancy Clanton,
> David Crawford recommended me to ask you, when I looked around (at the
> European DarkSky symposium in Lucerne) to find somebody who has an
> experience with lighting of slopes for downhill skiing. He was sure you
> have.
> A National Park in northern Czechia demanded an Environmental Impact
> Assessment concerning a project to light one slope there, and I am in fact
> the only Czech expert in environmental consequences of outdoor lighting.
> A colleague from Catalonia said me that ski lighting will be forbidden
> there. This is of course the most environment-friendly possibility.
> However, it would demand strong arguments and might be very unpopular in
> Czechia -- there are some lit slopes already, even if not in national
> parks. I'd prefer some compromise solution to show, that light pollution
> prevention does not imply an end to the nowadays way of life, but rather
> brings a new quality to it.
> Therefore my draft recommendation has been to use decent amount of light,
> giving the snow the luminance around the top limit of the values
> recommended for roads, namely not exceeding 1 cd/m2. Even such a luminance
> of a long slope would illuminate substantially a vast area on the opposite
> side of the valley.  Some five lux of horizontal illuminance should give
> that 1 cd/m2 perhaps, even with the least white snow. The skiers
> themselves would be illuminated more on the average, thanks to the light
> from the snow; even in places with no direct vertical illumination they
> should be lit by some two lux. I suppose that such values should do, if
> the light from the luminaires above 75 degrees from the slope will be kept
> to minimum (i.e., with more than FCO demands).
> The project mentioned however an average horizontal illuminance of 20 lux
> for each evening, with a possibility of 100 lux for occasional
> competitions. 20 lux is mentioned in some technical standard for skiing.
> If I compare it with the recommended 4 lux for areas with many pedestrians
> and cyclists (cyclists are going more often in opposite directions),
> it seems to be an overkill to me. The slope has an only simple lift, so
> the traffic on the slope will be kept low.
> Another argument for not so large light levels is, that the surrounding
> paths won't be lit -- the lift itself (being divided from the downhill
> slope by a strip of forest) and the paths (some are in a dense forest) to
> the other parts of that skiing resort. With too much light on the slope, a
> proper adaptation to move safely on those paths would demand too long time
> to happen in reality. In view of this fact, perhaps 2 lux horiz. illum. on
> the slope would be better than five.
> The owner argues however that some previous experience showed, that even
> 20 lx is not enough, that there have been some collisions. My answer was
> they have been quite possibly due to glare. The more dangerous as the
> skiers can carry glasses with snow or drops on them. Low glare should be
> more productive than lots of light.
> I'd like to adhere to the 1 cd/m2 limit, as we plan to put it into the
> Czech regulations, for all cases where safety standards don't demand more.
> I would not say that 20 lx for skiing is a safety standard. If it would
> be, than the skiing on slopes with no artificial lighting should be
> abandoned even before sunset on the most heavily overcast days (say, with
> just some man-made snow on the slope and a dark landscape elsewhere), but
> all lifts operate till sunset in December and January. The more because
> the omnidirectional light from an overcast sky hinders recognition of any
> shapes on the slope, unlike sunlight or light from luminaires.
> But, your experience and opinion would be most authoritative for me. If
> you would agree with the low light levels, than that skiing slope could
> become a landmark in sustainable sports lighting. Otherwise I would rather
> recommend to avoid such a disturbance amidst a national park (even if
> there is a town in its centre).
> sorry for a long letter,
>  your sincerely
>  Jenik Hollan, IDA Czech Republic