# Blue lights and fast food
**URL:** https://boards.straightdope.com/t/blue-lights-and-fast-food/268987
**Category:** Factual Questions
**Created:** [October 13, 2004, 12:11pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987 "2004-10-13T12:11:27Z")
**Posts on this page:** 15
**Page:** 1
### Author:  [@Baluchitherium](https://boards.straightdope.com/u/Baluchitherium)
#### Post date: [October 13, 2004, 12:11pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/1 "2004-10-13T12:11:27Z")
Hi,
I’ve noticed that a number of fast food restaurants have a single, pale-blue light (often fluorescent) mounted behind the serving counter. Because there is only ever one, and its location is nearly always the same – about 7 feet high, wall-mounted, often to the left side – and, in restaurants with no relationship to each other (i.e. owned by different companies), it makes me think the purpose is functional, rather than decorative…
…but that functional value (if any) is really not obvious. It doesn’t produce enough light to actually illuminate anything, and in some cases, it is projected upwards.
I asked a store manager once, but she didn’t know. Does anyone have any idea?
Richard C
Kingston Ontario
---
### Author:  [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)
#### Post date: [October 13, 2004, 12:37pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/2 "2004-10-13T12:37:16Z")
Possibly a UV light disinfection device?
---
### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [October 13, 2004, 1:04pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/3 "2004-10-13T13:04:58Z")
I think you might be talking about bug zappers; flying insects are attracted to the blue light and electrocuted on a grid of wires that is placed in front of the lamp.
---
### Author:  [@Philster](https://boards.straightdope.com/u/Philster)
#### Post date: [October 13, 2004, 1:12pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/4 "2004-10-13T13:12:57Z")
Fire prevention. Marks an extinguisher or other shut off control that must be located quickly.
Someone else can chime in about why it is blue and the low light vision of the human eye.
---
### Author:  [@Colophon](https://boards.straightdope.com/u/Colophon)
#### Post date: [October 13, 2004, 2:10pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/5 "2004-10-13T14:10:55Z")
> [@Philster](#):
>
> Fire prevention. Marks an extinguisher or other shut off control that must be located quickly.
Nope, they’re bug zappers, as **Mangetout** said. The insects make a satisfying _bzzzzt_ as they get fried.
[These the kind of thing you mean?](http://www.rgk.co.uk/acatalog/RGK_Catalogue_Electric_Type_132.html)
---
### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [October 13, 2004, 2:24pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/6 "2004-10-13T14:24:12Z")
Some of them aren’t zappers, as such, but they are for insect control. Some of them have a sticky paper in them that the flies stick to when they fly into it.
---
### Author:  [@Balle\_M](https://boards.straightdope.com/u/Balle_M)
#### Post date: [October 13, 2004, 2:50pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/7 "2004-10-13T14:50:06Z")
> [@Colophon](#):
>
> Nope, they’re bug zappers, as **Mangetout** said. The insects make a satisfying _bzzzzt_ as they get fried.
Here in West Virginia, that’s known as dinner and a floor show. 😃
---
### Author:  [@jwc008](https://boards.straightdope.com/u/jwc008)
#### Post date: [October 13, 2004, 3:39pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/8 "2004-10-13T15:39:04Z")
> [@Colophon](#):
>
> [These the kind of thing you mean?](http://www.rgk.co.uk/acatalog/RGK_Catalogue_Electric_Type_132.html)
[This product](http://www.pestproducts.com/cento_fly_trap.htm) is closer to what I often see in restaurants. [More information here.](http://www.pestproducts.com/uv_light.htm)
---
### Author:  [@Elvez](https://boards.straightdope.com/u/Elvez)
#### Post date: [October 13, 2004, 4:02pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/9 "2004-10-13T16:02:09Z")
> [@Philster](#):
>
> Fire prevention. Marks an extinguisher or other shut off control that must be located quickly.
My guess is similar to this. Fire hydrents on residential streets are commonly indicated with a blue glued-on reflector on the street’s centerline. I’ll have a look at some fast food joints on my drive home.
---
### Author:  [@Ruby](https://boards.straightdope.com/u/Ruby)
#### Post date: [October 13, 2004, 4:06pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/10 "2004-10-13T16:06:28Z")
Is this a regional thing? I’ve been to a lot of fast food restaurants and have never seen such a thing.
---
### Author:  [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)
#### Post date: [October 13, 2004, 4:23pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/11 "2004-10-13T16:23:37Z")
I know what the OP is referring to. The bulb is _always_ hidden from view. To me this, with the sky bluish color, suggests an ultraviolet light.
Every one I have seen in white in color and resembles, IMO, an upside-down washroom paper towel dispenser. I have always assumed it was UV disinfectant but insect trap makes sense also. For some reason, I can’t find an online photo of what I’ve seen.
---
### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [October 13, 2004, 4:47pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/12 "2004-10-13T16:47:13Z")
> [@jnglmassiv](#):
>
> IFor some reason, I can’t find an online photo of what I’ve seen.
I’m pretty sure [this](http://www.ecolab.com/DailyProd/SERV_NON_ST_PAUL_MAT/119_im_2.jpg) is what you mean. You can’t see the bluish light coming out of the top in this photo, but this is exactly the sort of thing I see often in restaurants around here.
---
### Author:  [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)
#### Post date: [October 13, 2004, 5:06pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/13 "2004-10-13T17:06:42Z")
**Q.E.D.** has done it again. Granted, mine wasn’t an exhaustive search but nice. The type I had in mind is about half the width of yours but otherwise just the same.
A google image search for restaurant insect trap only returns 4 images and only three of those are somewhat relevant. Another place I’ve seen these are in hospitals. ‘Hospital insect trap’ (not the phrase) returns zero images. Some sort of trap conspiracy, perhaps…?
---
### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [October 13, 2004, 5:11pm UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/14 "2004-10-13T17:11:11Z")
Heh. Well, to be fair, the name of the company that makes (or at least maintains) them is silkscreened on the front of the ones I’ve seen. I just went to their website and poked around.
---
### Author:  [@Baluchitherium](https://boards.straightdope.com/u/Baluchitherium)
#### Post date: [October 14, 2004, 11:44am UTC](https://boards.straightdope.com/t/blue-lights-and-fast-food/268987/15 "2004-10-14T11:44:49Z")
Thanks kids…I’ll sleep better now, thanks to your research!