VISUAL ILLUSION RED/BLUE?

I 26

Member
Sep 9, 2010
315
Vancouver, Canada
Okay, it's been a while since I've been here, so I don't know if this is REALLY the correct section, but there is something I've been meaning to ask...


...Why is it when I approach a police unit with a red/blue LED lightbar (local police use red/blue Liberties) the blue light seems to be emitted from a point significantly lower than the red light? This is most notable from a distance of several hundred feet. The red light appears level with the lightbar, but the blue light seems almost to be coming out of the windshield.


If anyone can shed some light on this, please do! I'm quite curious.
 

unlisted

Lifetime VIP Donor
May 20, 2010
7,333
NA
Hey, at least you don't see purple..


and I think its simply the way your eye/mind perceives the light. Does this happen in daytime, night or both for you?


and totally the right section.
 

SSgt Elmer

Member
May 21, 2010
177
NE WI, USA
It's not just you, I notice that too. I think the answers above are right, though I don't claim to understand it lol.
 

ryanm

Member
May 20, 2010
587
Arkansas
I've noticed the same thing... even with blue-only bars. The light flash doesn't seem to be even with the lightbar at all.
 

NPS Ranger

Member
May 21, 2010
1,988
Penn's Woods
It's the difference in refraction of the monochromatic light through the thickness of the cornea. Think of a prism. Different colors diverge from the angle of incidence depending on the wavelength of the light.
 

fp13-2

Member
May 20, 2010
358
Harrisburg, PA
If you wear glasses, it can be more noticeable. Move your head up and down and the red/blue will swap places being higher and lower. It's just due to them being different wavelengths of light.
 

I 26

Member
Sep 9, 2010
315
Vancouver, Canada
So I get it! Because red is located higher than blue in the light spectrum the blue appears lower than the red? So, for instance, green is located somewhere between red and blue...so if we had a Red/Green/Blue lightbar, the green would appear at a level between red and blue?


So why is this only visible with LED? Is it because of the narrow intense beam as opposed to a halogen which throws off a wider floor of light?


And yeah, it happens both in day and night time...and I do wear glasses, yes.


Thanks for the responses!
 

I 26

Member
Sep 9, 2010
315
Vancouver, Canada
I was originally toying with the concept that for some reason the factory intentionally aims the blue lower for some reason...but that doesn't really make sense now that I think about it.
 

EVModules

Member
May 16, 2010
864
Deer Park, WA
Oy, none of you took science in school?


You're just drunk, leaning, and walking in circles. :cool:


Actually, just about every vehicle's front glass slopes, thereby shifting light that shines through it much like a flashlight hitting the surface of water at an angle than straight on. You can notice the difference by sitting halfway out of the car and look downrange between the glass and directly outside. it's way more pronounced looking in prismatic rear-view mirror because it's essentially a very flat prism with a silver coating on the back.
 

nerdly_dood

Member
Jun 15, 2010
2,312
Georgia
unlisted said:
Hey, at least you don't see purple..

and I think its simply the way your eye/mind perceives the light. Does this happen in daytime, night or both for you?


and totally the right section.
In bright sunlight I don't even see the blue, but if it's not very bright out then I do see the blue lights "lower" than red ones. For that reason I'd like to someday see a Whelen Freedom with blue LEDs on the top level and red ones on the bottom level so they seem like they're on the same level (with a flash pattern that avoids the appearance of purple of course)


This applies to ALL blue LEDs and ONLY blue LEDs. No matter what kind of material they're shining through (a plastic lightbar lens, or a glass car window) or whatever angle the material is at, that always happens. And it doesn't happen for blue strobes or halogen lights at all.
 

Gonzowerke

New Member
Sep 5, 2010
9
I see purple, from a mile or so away(only at night). When I get within say, a 1/4 mile, it resolves to blue and red. I see the same effect on bikes with blue dot lenses in the rear.
 

nerdly_dood

Member
Jun 15, 2010
2,312
Georgia
Gonzowerke said:
I see purple, from a mile or so away(only at night). When I get within say, a 1/4 mile, it resolves to blue and red. I see the same effect on bikes with blue dot lenses in the rear.
When I see a bike with LEDs in the back flashing in an X pattern, I can't even see that they're flashing at all from a distance, only up close can I see that they're not steady-burning.
 

PFD34Explorer

Member
Jan 29, 2012
18
CA
Noticed this lately & brought it up to a buddy. He noticed the same. Why is it Blue LEDs seem to be lower than red LEDs? It doesn't matter on the application (mirror lights, lightbars) they all appear the same. Are they adjusted to different heights for coverage at all height angles for different sized vehicles?


Also, If a lighthead that has previously programmed patterns put onto steady burn, then wired to a Whelen LED flasher, does the whelen flasher control the patterns? I am thinking of doing this with some strobesnmore light heads.


Thanks for any insight!
 

bluestinger90

Member
Jun 5, 2010
657
BC / California
Long story short, our eyes are not good with blue light. I have personally seen this with red and blue lights, but do states with all blue led lighting experience the same thing?


Coding Horror: Blue LED Backlash


"Blue LEDs really are brighter than their old-fashioned red and green counterparts. Barney O'Meara, vice president of Canadian LED manufacturer The Fox Group, said blue LEDs have at least 20 times the luminous intensity of old-fashioned red and green indicators. O'Meara said his company has developed technology to manufacture low-intensity blue LEDs.


"Blue tends to cause more discomfort and disability glare than other, longer wavelengths," said Dr. David Sliney, an expert on the harmful effects of bright light sources at the U.S. Army Center for Health Promotion and Preventive Medicine in Maryland. Sliney said the eye's lens cannot focus sharply on the blue lights. While red or green light is focused precisely onto the retina, blue light is focused slightly in front of it, which causes a distracting halo around bright blue lights.


In addition, blue scatters more widely than other colors as it passes through the eyeball, Sliney said. Together, these two effects cause the intense blue light from a point source, like an LED, to spread out across the retina, interfering with other parts of the scene. It's called dispersion: Blue's shorter wavelength makes it refract at a greater angle than, say, red or green.


Also, human vision becomes far more sensitive to blue when ambient light levels are low, a phenomenon known as the Purkinje shift. So a blue light that is merely eye-catching on a brightly lit store shelf can become dazzling when the lights are low, such as when watching a movie on a laptop in a dimly lit room.


Some researchers report that, at night, even low-level blue light may be enough to trigger recently discovered receptors in the retina that can depress melatonin production, disrupt sleep patterns and suppress the immune system."
 

unlisted

Lifetime VIP Donor
May 20, 2010
7,333
NA
PFD34Explorer said:
Noticed this lately & brought it up to a buddy. He noticed the same. Why is it Blue LEDs seem to be lower than red LEDs? It doesn't matter on the application (mirror lights, lightbars) they all appear the same. Are they adjusted to different heights for coverage at all height angles for different sized vehicles?

Also, If a lighthead that has previously programmed patterns put onto steady burn, then wired to a Whelen LED flasher, does the whelen flasher control the patterns? I am thinking of doing this with some strobesnmore light heads.


Thanks for any insight!

Threads merged. Please use the search function before creating a new thread.


Thanks!
 

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