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I recently visited London and noticed some pedestrian traffic lights are covered weirdly so they're only visible from some angles.

traffic lights in trafalgar square

Looking it up in a search here didn't bring up any results.

Does anyone know why they're going through the trouble to do this?

Benjamin Gruenbaum
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    Looking at this photo made me thinking of "grills", and after searching for "traffic light grill cover", I got more keywords like "louvred covers/blinds" and "slatted covers". Hopefully that could be useful for those who are interested in searching further... – Andrew T. Sep 17 '18 at 03:07
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    Your question already contains the answer: it's so that they're only visible from some angles. The point being that the light controls one particular stream of people and they don't want other streams thinking "That light means me" when it doesn't. – David Richerby Sep 17 '18 at 11:11
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    @seadoggie01 It's the UK. There is no sun. – Mast Sep 19 '18 at 07:41
  • I've even seen lights with bulbous lenses or fresnel lenses in front to control which approach road sees the light. Only seen where two roads meet at an angle well less than 90 degrees, perhaps as close as 20-30 degrees. – Criggie Sep 20 '18 at 05:12
  • This is completely normal on traffic lights throughout the world. There is no difference whatsoever in Europe, Asia, Americas. – Fattie Sep 20 '18 at 06:12
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    I'm voting to close this question as off-topic because traffic light technology is totally unrelated to Travel. (The light-louvres mentioned are a commonplace on all traffic lights everywhere.) – Fattie Sep 20 '18 at 06:13
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    They may be common in some parts of the world, they are surely not common all over the world and I feel this Q was closed without good reason. – Willeke Sep 23 '18 at 10:20

3 Answers3

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You are most likely to find the green light with shades on the far side of a pedestrian crossing with a safety island (i.e. a two-part crossings, most often offset to each other), as illustrated below (the o are the traffic lights):

     Kerb
_____o------____ <- Shaded light
     .     .    >>> Traffic goes this way
     .     .
_____|=====o____ The safety island
   o=====|
   .     .      <<< Traffic goes this way
   .     .
___------o______ <- Shaded light
     Kerb

Due to road layout and light configurations, sometimes it is only safe to cross half of the road (up to the safety island). The shades ensure that you do not mistake the green light on the island as the signal to cross the entire road - you can only be sure that it is a green light (but not a broken light, which the general highway code on crossing a uncontrolled crossing kicks in) once you are on the island.

Similar shades are installed on traffic lights for vehicles to reduce the risk of drivers running into an intersection thinking it is a green, when the light meant for the driver is showing red.

I do not have a written source to back up what I said above, though I was told this by my driving instructor when I learnt to drive in London a few years ago.

B.Liu
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    I believe that if the pedestrian light does not cover crossing teh whole road that the two crossings must be offset from each other. ie if the two crossings are aligned as in your ascii diagram that there shouldn't be separate lights covering each half. I do agree with the general comment that they are to prevent the wrong people from seeing them though. – Chris Sep 16 '18 at 21:40
  • @Chris A request for clarification - when you say 'offset' do you include cases where the two crossings are at a very slight angle to each other? – B.Liu Sep 17 '18 at 06:19
  • @Chris Actually, after more thinking I don't believe the two crossings must be offset. I spotted a few counterexamples on my way to work today, and shall do more research on this tonight to see whether it is not true or there exist sloppy implementations. – B.Liu Sep 17 '18 at 06:54
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    Rule 28 in https://www.highwaycodeuk.co.uk/rules-for-pedestrians-crossings.html explicitly says that if the crossings are not in line they are separate crossings. It does not say anywhere that inline crossings can be two separate crossings for light controlled and the fact that rule 28 exists implicitly suggests that inline crossings are a single crossing. That is also all the information I have on the technical rules for what makes a crossing offset. – Chris Sep 17 '18 at 08:27
  • I'm not sure what you have in mind when you talk about crossings at an angle to each other - since crossings in my experience are always perpendicular to the road I'm wondering if you are considering two crossings on roads that meet next to the crossing in which case I would imagine that if they are separate roads they would be controlled separately (ie not considered the same crossing). – Chris Sep 17 '18 at 08:28
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    @Chris See the pedestrian crossing at Pancras Road near Euston Road for a inline pair of crossings, and the junction between City Rd and East Rd for a slightly angled pair of crossings. – B.Liu Sep 17 '18 at 08:44
  • Let us continue this discussion in chat. – B.Liu Sep 17 '18 at 08:47
  • If this is true, shouldn't the shades be vertical? – vsz Sep 17 '18 at 18:34
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    AFAIK the distinction between single and two-part crossings is not the geometry, but where there is a "refuge" (technical term) for pedestrians to wait between the two parts, which is inaccessible to vehicles - i.e. at a minimum it has "vehicles must pass on one side only" bollards at each end, and usually has a raised curb, guard railings, etc, as well. Any lights in the center of the road need to be protected from vehicles, which means that "central lights" and "a central refuge" go together in practice. – alephzero Sep 17 '18 at 20:13
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These type of shades are not restricted to pedestrian traffic lights. They are widely used in the UK when there are many lights controlling different streams of traffic around a junction.

Their purpose is to ensure that drivers (and pedestrians) can only see the lights that are relevant to them and avoid problems like traffic starting to move when another lane of traffic gets a green light.

The shutters are not always "horizontal" as in the OP's photograph. They may be "vertical," to prevent you seeing a light positioned to the side of the light that is relevant for you.

alephzero
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    They're also known as snoots, as in, they're snooted. In photography we use snoots to control light from flash guns. As in your answer, it's to stop lanes of traffic for which the signal does not apply from seeing and reacting to the light. – i-CONICA Sep 17 '18 at 12:37
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    The question only asks about the UK but these also exist in parts of the USA and I'm sure other areas of the world, all for the same purpose. – Steve V. Sep 17 '18 at 17:33
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    @SteveV. In the US (at least Seattle) I see traffic lights (but not pedestrian lights) with clear lenses on them instead of shutters/blinds and the lenses focus light so it's only visible in certain lanes and at certain distances from the light. – Dai Sep 17 '18 at 20:53
  • I believe this is the best and most concise answer. Very well explained and straight to the point. – TheBlackBenzKid Sep 18 '18 at 09:16
  • This does not make sense at all for horizontal shutters like the one in the question. – mastov Sep 19 '18 at 14:04
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We use these in the USA and that is the only place I have noticed them.

There are at least 2 general "shade" types, "visors" and "louvers".

  1. Visors: Horizontal "shades" like the ones you posted are most likely to block the sun overpowering the light as this intersection probably faces roughly East/West. They also come in a few other shapes/forms.

    The addition of a visor to a traffic-signal head that is in direct sunlight can improve visibility of the signal by providing additional contrast between the lens and the signal head. There are different types of visors including complete circle (or tunnel), partial (or cutaway) and angle visors. -Source

  2. Louvers: Louvers take many shapes but the most obvious is a vertical sort of "shade" like so. A Louver's purpose is to restrict the viewing angle of the signal. louvers

    The purpose of a louver is to block the view of the signal from another approach. They are similar to angle visors but are better in limiting signal visibility to a narrow cone to the front of the signal. - Source

It is also worth mentioning that some visor designs work well for the same purpose as Louvers, however Louvers don't generally do a very good job as Visors.

DJSpud
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