Interesting – have not been in a coal mine, but have been in the middle of Ontario many times on an overcast night.

Your peripheral vision works differently than straight forward vision – according to a colleague who has a PhD in this stuff – and I think he's right. If you want to see something when it's near pitch dark, don't look where you think it is, but let your peripheral vision find it (if it can).

I don't propose to understand why, but vision is an interesting gift we've been given.

Thanks for the anecdote; JohnS.

I believe a large number of materials electrofluoresce under stress eg being squashed underground and in reverse as mining changes the sress distribution. Also many bacteria, as on human skin, do the same. Meanwhile the optic nerves and brain trigger false lights like crazy when you just close your eyes.

Edited By Bazyle on 15/02/2014 17:59:57

Could it be piezo-electric discharges caused by extreme pressure on the likes of quartz rock? Ian S C

Peripheral vision is important when you are driving, that is the bit that you steer by, forward vision sets the course but the accuracy of missing things is a lot closer!

There is a phenomenon. .called triboluminescence..basically direct stress to light from materials. . ( duct tape does it)…it would be facinating to think that rocks in mines emit light possibly indicating stress in the mine walls…

Interesting that MW remembers very low level colours. Cones come in three colour sensitivities, Red Green and Blue and are clustered together, they don't work at all at low light. There are roughly 20 times as many rods which do go down to single photons when very well adapted. So for normal humans as light level drops we see less colour, red tends to dim first, the peak sensitivity at green- blue gives way to grey at around 100 times min detection level. At very low light levels we cannot see colour at all, you need a telescope or binoculars to see the colour of stars.

Broadcast Colour TV has taken advantage of these properties for years, We have only ever watched black and white pictures with the coarse detail coloured at lower bandwidth, matches out eyes!

There is a third type of photo receptor – not many people know about so handy for the pub quiz- photosensitive ganglion cells which respond to high general illumination.

Billy.

Potholing? A very good friend of mine used to go caving when he was younger. He used to like to tell the story of how after a session down a pothole (I think it was Gaping Gill but memory is not so good these days) each potholer in the group was hauled to the surface by a windlass while seated in a chair like contraption. Only one person at a time could make the trip and on this occasion my friend had drawn the short straw and was the last to be pulled up.

As the last but one person was lifted off from what was a vast underground cavern, my friends helmet light flickered several times and finally went out. He was left sitting in the profound darkness of an underground chamber but was relaxed in the knowledge that the "chair" would return to lift him out -eventually.

He painted a word picture of himself sitting in the blackness with the sound of falling water echoing from the walls of the cavern, the occasional clatter of falling stone and a profound sense of being alone. He would explain at this point that in a situation like this your life is entirely in the hands of "them up top".

He goes on " As I sat there, I fancied I could see – now and again – a faint light flickering in my peripheral vision but when I turned to look in the direction of the light it disappeared." Gradually though, the light becomes stronger and it seemed to be coming nearer flickering as a candle would. This cannot be possible my friend explains, I was the only person in that pothole so who was carrying that light?

My friend is not the sort of person to be intimidated, he is a down to earth scientist – a mathematician expert in aerodynamics and probably the UK's leading expert on the Russian ekranoplan, a devout atheist and scoffer of the paranormal yet he admits that as the light gets ever closer the hairs on the back of his neck begin to stand.

With a clatter the rescue "chair" arrives and in the dark he straps himself in, yanks the rope to signal "lift" and begins his ascent. On his way up he looks down and sees the flame stationary where he had previously been sitting.

He looks around us goggled eyed lot over our pints at our table in The Black Horse and remarks "I was a little relieved", and we believed him!

Rik

There was a program on Discovery about a year ago using marine very low light imaging. They had some state of the art cameras working in a very dark night at sea. The wake from the boat glowed brightly, a kind of phosphorescence from bacteria in the sea when hit by the pressure wave. Almost everything glowed underwater, many creatures were light producing -when they wanted to be.

At very great sea depths it is always thought of as being very dark, most creatures at these levels ( and cave dwellers) are not pigmented or marked. Many are blind. There is the most extraordinary creature of the deep , the Giant Squid which has by far the largest eye knowen at around 12" diameter. That eye would not have evolved if the Squid did not gain an advantage from it's low light performance.

Our eyes are relativly insensitive and slow to adapt, it can take up to 30 mins – dependant on life style and health- for the human eye to reach maximum sensitivity, older eyes tend to have smaller fully open apertures too. We also tend to avoid extreem dark wherever possible, we have developed to avoid situations where we are at a great disadvantage to other preditors which is a pretty good idea! So we may well lack detailed knowledge of common low light events , let alone the unusual ones.

As a wiser man than me said " It's only the hole in the ear that lets in the fear, that and the absence of light"

Billy

I too am intrigued Ian, maybe Geoff has " seen the light" ??!!

Martin.

Michael, you mention radio activity, while in England the last time(1984) I stayed with an uncle who was CEO of British Nuclear Fuels, and among other things we talked of, he was saying that they had been testing coal fired power stations for radiation, and were shocked at the high level of radiation in the coal, far above that allowed in the atomic power stations of the time. So radiation could be quite high in a coal mine.

He also mentioned how one power station had a bit of an emergency, a group tour went through the station, and on exiting everyone gets scanned, and one woman went "off the clock", it was found that the jewellery she was wearing was "hot", it was an antique broach, with lapis lazuli stones, and these were the source of the radiation. So its around us even when we least expect it. Ian S C

Bananas

.and Brazil nuts.