Switch or lever seen at night only

[Mmm786]

Hi I am stuck writing a novel. The protagonist is stuck outside a building being chased by the bad guys. He already tried to get into the building during the day but there was no way in. There are no doors windows or anything. My idea was he sees a lever or switch using a uv torch he is carrying but is this scientifically possible? Can anyone think of a better solution? The important thing is they are able to get in because it's night if that makes sense. Any help would be much appreciated. Max

[Mike-from-the-Bronx]

How about something low tech like this:

The switch is hidden behind a loose brick.  During the day the loose brick is indistinguishable from all the other bricks that make up the building.  But at night, because the interior of the building is well lit, a sliver of light shines through a crack above the brick.

The protagonist would see the light, pull out the loose brick, flip the switch, replace the brick and toss some loose dirt into the crack so the bad guys would not see and follow.

Edited December 10, 2019 by Strange
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[StringJunky]

24 minutes ago, Mmm786 said:

Hi I am stuck writing a novel. The protagonist is stuck outside a building being chased by the bad guys. He already tried to get into the building during the day but there was no way in. There are no doors windows or anything. My idea was he sees a lever or switch using a uv torch he is carrying but is this scientifically possible? Can anyone think of a better solution? The important thing is they are able to get in because it's night if that makes sense. Any help would be much appreciated. Max

There could be a brick in the wall that fluoresces in the light of the torch and when he puts his hand on it there is an infrared detector embedded in that senses the heat and a door, covered in a brick facade, opens inwards.

[zapatos]

Perhaps the lever or switch can only be seen at night (perhaps under a full moon) due to the Purkinje effect.

Quote

The Purkinje effect (sometimes called the Purkinje shift) is the tendency for the peak luminance sensitivity of the eye to shift toward the blue end of the color spectrum at low illumination levels as part of dark adaptation

https://en.wikipedia.org/wiki/Purkinje_effect

[iNow]

Make the opening surrounded by pollen emitting plants. Since lightning bugs eat pollen, they could light up the opening at night. Only works in spring and summer months tho

[Mmm786]

Thanks guys what kind of things show up under a UV light? 

[StringJunky]

1 hour ago, Mmm786 said:

Thanks guys what kind of things show up under a UV light? 

Yo can get uv paint

[swansont]

If the criterion is only seen at night, the switch (a tile that you push, for example) can light up because of an optical sensor that senses it's dark out. Much like how streetlights turn on.

If you insist on being UV sensitive, as StringJinky says, there are UV paints, and there are other materials that fluoresce. There are a number of minerals that fluoresce under UV but some look quite ordinary under visible light

https://geology.com/articles/fluorescent-minerals/

[Strange]

It could just be dimly lit so that it is not visible in daylight but becomes visible as the ambient light level falls.

If it glows because of UV, do you want this to be deliberate or by lucky chance (there are a lot of materials that glow in UV light even though they are not "designed" to do so; tonic water is a classic example).

[Mmm786]

Thanks I want it so that anyone following can't see it with the naked eye that's why I went down the UV light route. Any better suggestions would be appreciated. So far the lever option sounds the easiest. 

[Strange]

I just unhid* a post from Mike-from-theBronx, which you might have missed, that I actually think is a pretty neat idea.

* Because reasons. Nothing to worry about.

[swansont]

You could go with something involving polarized light, and the protagonist is wearing sunglasses (that typically have polarization filters in them) but others are not. Probably works better in daylight, though.

[Ghideon]

Low-tech idea, not using UV, variant of the above from Mike-from-the-Bronx: The protagonist uses raking light* and notice that one brick is not aligned with the rest of the wall. The brick is loose and hides a button. Or the brick itself is the button. Reason for the brick not to be aligned could be that it was not properly placed back by a previous visitor.

UV idea: One brick is not made of same material as the rest. In visible light it not possible to tell the difference but In UV light the fake brick (the button) looks slightly different. It could by mistake** contain minerals mentioned by @swansont

 

 

*) I had to search for the English term: https://en.wikipedia.org/wiki/Raking_light
**) I have not researched if that makes sense scientifically

[Mmm786]

Yeh that's a good idea I was thinking one of the bricks could be made of, or includes, a fluroscent mineral. Although it looks the same as the other bricks to the naked eye, it's a different colour under a UV torch? Is that plausible? 

[Ghideon]

Another simple attempt: For instance some laundry detergents and cosmetics are visible in uv light. If the button for activating the mechanism is not regularly cleaned (or cleaned using "wrong" products) chances are that an inspection with an uv light would reveal the button since it may have more contaminations than the surrounding area. Those contaminations might not be visible in daylight.

The idea may be useful if you want the discovery of the button to be by mistake rather than a deliberate design. 

 

1 hour ago, Mmm786 said:

Although it looks the same as the other bricks to the naked eye, it's a different colour under a UV torch? Is that plausible? 

 

A different color under uv light is plausible. Here is an example picture from https://en.wikipedia.org/wiki/Fluorescence:

 

 

 

[Mmm786]

Hmmm the cosmetics and detergent theory could be quite good as I want them to find the switch or lever by mistake. Which cosmetics would you recommend?