Why does the orange color in some fabrics stand out so prominently?
I noticed a chap down the street with an orange hunting cap. It was the brightest thing on the block. Then I went to the 99¢ store and the brightest thing in the store was an orange safety vest.
What is it about this orange that makes it stand out so prominently?
The Wikipedia article on safety orange suggests that it is by design and that this hue was chosen specifically because it contrasts so well with sky blue (azure).
A special dye.
It takes in ultraviolet light and reflects it back in the visible range. Not very much mind you, but enough to make it highly visible.
Safety orange is created by a dye that is fluorescent. It absorbs light in the UV and blue parts of the spectrum and re-emits it as orange light. As a result the orange colour really *is *much brighter than any other colour around. It isn’t just an illusion, there really are more orange photons being emitted than is possible for photons in any other part of the spectrum.
A typical orange dye will reflect only photons (read light) in the red-yellow parts of the spectrum. Any other photons that strike the dye are absorbed. As a result an piece of fabric dyed orange will be much, much duller than a piece of white fabric, since the white reflects all light (essentially).
A safety orange dye will also reflect light in the red-yellow parts of the spectrum. However it also *captures *any light from the rest of the spectrum, including the invisible UV parts. It doesn’t reflect this light. Instead the captured light gets converted from it’s original colour into red-yellow light and is then re-emitted by the dye.
As a result safety orange is much brighter than any other object in the same light. In sunlight it is even brighter than white material because of the additional light gathered from the invisible UV. In artificial light it is slightly less bright than pure white, but because it is a monolithic colour it is still much more visible than white.
Which doesn’t really explain why it is brighter than surrounding objects. Even in the middle of a room full of other orange objects, safety orange is highly visible.
It’s not just the UV, it’s all the rest of the spectrum. Any higher energy light gets converted into red-yellow. This is why safety orange remains highly visible even under artificial light.
This is also why you can get fluorescent orange, yellow and red dyes, but not fluorescent greens and blues. Fluorescent dye can’t convert up the spectrum. Because blue is already high energy, the dye can’t convert red into blue. But it can strip energy from blue and convert it into red easily.
Eh? There are plenty of green and blue fluorescent dyes. Granted, you’re right about the physics – those dyes will absorb UV light and re-emit blue or green. The blue or green fluorescence isn’t very strong under most ordinary lighting conditions, but that’s just because there isn’t much UV (proportionally speaking) in sunlight, and almost none at all in indoor lighting. If you’ve got a UV light source like a black light, you can get bright blue or green fluorescence.
When I say “you” I mean the man on the street.
You and I can order fluorochromes of any colour we like from Sigma, even UV if we wish. The average person can get fluorescent orange dyes at the local craft store, but not blues and greens.
I’ve always wondered why hunters can see each other so well in orange, but deer can’t see orange-clad hunters? Are deer and other wild game blind to orange?
Simply spotting the color is only one part of the reason the bright orange is used. I think the other has to do with the fact that hunters are (hopefully) only going to shoot at something that they’ve lined up in their sights: The orange is to make it obvious that whatever you’ve got lined up isn’t a deer.
I’m still pretty sure you can buy blue or green fluorescent paints at a craft store. They’re just pretty disappointing for anything other than black velvet paintings…
I have a lime green windbreaker meant for wearing while bicycling which seems to be exceptionally bright. This is especially the case on heavily cloudy and foggy days. It just seems to grab more than its share of light. I expect it also has fluorescent dye.
Yes.
Some authorities think they are completely color blind, others say it’s mainly in the red-green spectrum. Either way, the orange does not stand out to them.
But with it being brighter than white light, you’d think it would.
Deer tend to be woodland and forest animals. Their natural environment has dappled light patterns. No matter how bright a shirt is, it won’t be brighter than an area in direct sunlight.
Or to put it another way, a mirror is also much brighter than white fabric. How easily could you see a mirror in woodland (assuming it wasn’t directly reflecting sunlight into your eyes)?
Some materials actually do this.
Like what? Wouldn’t they have to lose energy to do so?
I know pretty much zero chemistry so I’d believe it, it just seems intuitively very surprising.
Yes, it loses energy in the process. Note that any object radiates, losing energy in the process (though gaining through absorption too).
The phenomenon, called “anti-stokes shif”, is mentioned here.
I think it’s because which gets reflected back in the visible spectrum.
Sort of. The substance in question has to be able to absorb the incoming radiation and the absorption has to be close enough to the surface that the emitted light is free to escape.
But it’s true that excitations of different energies lead to (mostly) the same emission.
Also add “have a high enough quantum yield” to the requirements there.