Hues from AR coats

[Henchos]

having recently come across a Dipensing optican examiner,he asked me why is a blue hue better for drives rather than green-is it simply because it lets more the traffic light colours thro and away with annoying blue light?He also pointed out that hues matter for VDU users,i think he was just being too technical?

[For-Life]

having recently come across a Dipensing optican examiner,he asked me why is a blue hue better for drives rather than green-is it simply because it lets more the traffic light colours thro and away with annoying blue light?He also pointed out that hues matter for VDU users,i think he was just being too technical?

Apparantly the blue hue lets in more light transmission. Essilor advertises that their green hue allows in 99.2 percent and their blue 99.6 percent.

[coda]

For-Life is mostly correct. The luminous transmission (i.e. light transmission corrected for eye sensitivity) is very slightly higher for most blue AR designs than most green AR designs. Remember, however, that the lens material absorbs enough light that the difference is not perceptable to the wearer.

As far as color distinction is concerned the difference in transmission between a green design and a blue design is meaningless.
To answer Henchos' question: I think the examiner was being a prat, from the standpoint of the wearer there's no difference (including looking at traffic lights, CRTs, etc.) and the difference in the amount of very low wavelength visible (i.e. that nasty fuzzy blue) the green design actually reflects more than the blue design (in most cases).

[HarryChiling]

To really understand the hues you must first understand how AR coats work. It works by causing destructive interference. If the thickness of the coating is 1/4 of the wavelength of light the this light the reflections off of the surface of the lens and the AR coat cancel each other out. However If the coating is 1/2 the wavelength of light then they coumpond each other this is called constructive interference.

Ok, thats out of the way. The visible spectrum is 380 to 760 if we were to do 1/4 of 760 we get 190. This as you notice is also 1/2 of the 380. 760 is the between 660 ad 760 is or reds. You are creating destructive interference on this wavelength of light, but on the 380 to 400 range we have our violet. You are creating constructive interference on this wavelength. This coating is going to give off a violet reflection.

you can do it with any thickness of coating 1/4, 3/4 or your mirrors 1/2 and 1. they are all going to cause destructive and constructive interference somewhere on the spectrum. The AR manufacturers use this to create the different hues in the coatings.

I would not say that any specific hue is better than another, however one could argue that if you have desructive interference off of the internal back surface off the lens. The small amount of that spectrum that would again reflect off of the front internally would be eliminated. You could argue that certain hues would decrease the transmission of that certain spectrum of light. This would be too small of a difference to even consider a benefit.

[rolandclaur]

Let's not forget that most contact lenses are visibly tinted blue because it transmits more light under scotopic and photopic conditions than any other tint. Thus when an a/r coating with blue reflective hues are used, the level of transmission is just a smidge higher..

[chip anderson]

Rolandcur:

Most contact lenses are tinted blue:
1) So that it can be found on the eye and in the case.
2) Contact lens companies are now run by bean counters instead of opticians and blue was the most popular color in rigid lenses (because you could change blue eyes and you couldn't do much with dark eyes). Blue is the worst color one could use from the standpoint of color preception/transmission, gray being best but in the soft lens business the greatest market gets the most attention. Used to be the patient with the greatest need came first.
3) Conditons that really need attention in contacts now wait until primary markets are met and niche(s) are the remaining market.........

[rolandclaur]

wow chip.. i was under the impression that blue was the best color for light transmission for the wearer.. Gray really is? Can ya give me some info as to why? Thanks

[rolandclaur]

Maybe a reason most contact lens companies chose not to use gray as a color for a contact lens tint is the same problem that glass recyclable companies have to re process glass... Just as a brown glass container would be very unappealing to the consumer, I would assume that a gray contact lens would also have the same impact