Tunnel light - why white?

[Proper Job]

......... and that's not just with tunnels either

[GUMPY]

 

Nav lights are required on all of the Thames (tidal and non tidal) if you use your boat after dusk. I don't believe there's a requirement if you travel during daylight or most narrowboats would comply

Also in conditions of poor visibility (fog, mist, rain, snow etc) even during daylight hours.

[Nightwatch]

Ours is Brass coloured.

 

Martyn

[Chalky]

The best light depends on the lighting conditions. In daylight you're using Photopic vision and you're eyes are most sensitive to Red and Green (i.e. the colour of things you'd eat when swinging from the trees). At night you're using Scotopic vision and you're most sensitive to Blue / green - the colour of moonlight. At night th ewye is insensitive to red light which is why its used for things like cockpit lighting . Ideally the tunnel light should be about 508nm which would take advantage of this. The difference is very marked. When the eye is fully dark adapted it's 2.5 times more sensitive to a scotopic light than it is to white light. This is one of the reasons why HID lights appear brighter - they have a large blue content which halogen lights don't.

[Proper Job]

The best light depends on the lighting conditions. In daylight you're using Photopic vision and you're eyes are most sensitive to Red and Green (i.e. the colour of things you'd eat when swinging from the trees). At night you're using Scotopic vision and you're most sensitive to Blue / green - the colour of moonlight. At night th ewye is insensitive to red light which is why its used for things like cockpit lighting . Ideally the tunnel light should be about 508nm which would take advantage of this. The difference is very marked. When the eye is fully dark adapted it's 2.5 times more sensitive to a scotopic light than it is to white light. This is one of the reasons why HID lights appear brighter - they have a large blue content which halogen lights don't.

 

Interesting stuff

 

What's 508nm ?

[dor]

508 nanometres, i.e. the frequency of the light.

[Kwacker]

I find a 40w Spotlight pointing at 90 degrees to the boat, shining on the right hand tunnel wall is much more useful to me as a steerer than the actual tunnel light, which is 50 feet away and looking up and to the right.

The reflected light allows me to see the deck, curing the spacial awareness problems I was experiencing.

[Naughty Cal]

"(9) Any vessel passing by day or by night through a tunnel exceeding four hundred and forty yards in length shall display in the forepart of the vessel a visible white light. "

[Proper Job]

440 yards = 1/4 mile = 400m

[Timleech]

 

Interesting stuff

 

What's 508nm ?

 

Well I suppose it could be 508 nautical miles (= 585 statute miles), but I doubt it.

 

508 nanometres, i.e. the frequency of the light.

 

To be pedantic it's the wavelength of the light, though the frequency is inversely related to wavelength

 

Tim

[Neil2]

 

.......................................

 

It depends what sort of boater you are. The boards at the end of the tunnel will tell you to put the light on, along with stuff about naked lights, canoes and mythical transit times. If I can barely distinguish the tunnel from a bridge at a distance (Newbold or Gnosall for instance) I often throw caution to the wind and leave the light off

 

Richard

Yes where do they get these estimated times from? I never saw one that bears any resemblance to actual transit times maybe they date back to the 1800's.

 

BTW found an old copy of BW regs which states no light required for tunnels under 440 yards, I presume something like this would still be in force.

[Chalky]

 

To be pedantic it's the wavelength of the light, though the frequency is inversely related to wavelength

 

 

Velocity = Frequency * Wavelength

 

Velocity of light = 3 * 10^8 m/s

[RLWP]

Yes where do they get these estimated times from? I never saw one that bears any resemblance to actual transit times maybe they date back to the 1800's.

 

I always take them as a challenge. Halving them for a start

 

Richard

[Peter X]

As has been pointed out, that 508nm is a wavelength in nanometres, which according to this:

http://en.wikipedia.org/wiki/Light

would be in the green part of the spectrum.

 

Most light sources except lasers, whether natural or manmade, produce light spread across the spectrum rather than just one wavelength/frequency, e.g. the sun's white light is a mix of a wide range of colours, and like all stars it's also sending us a smorgasbord of other electromagnetic radiation outside the visible spectrum such as the UV that gives us sunburn. Man-made coloured lights are produced by two methods:

(1) generating more light in one part of the spectrum, e.g. sodium street lights were common because they were a cheap way to produce a lot of light and we lived with the drawback that it's mostly yellow.

(2) Filters, i.e. covering a light with something to block certain colours. An example would be the red plastic over a white light used to make vehicle rear lights.

 

Maybe it would make some sense to have some sort of colour coding of headlamps in tunnels, but the current rule is white and it would cost a lot to have everyone change. In my limited experience of passing through tunnels (only as crew, not steering) it can be hard to tell for a while if a light is a boat coming or going, or the end of the tunnel. But it doesn't matter too much as long as an oncoming boat follows the etiquette of not being too blinding, you find out soon enough what it is.

[Proper Job]

Not knowing what's coming is half the fun