Yes, my question was answered some time ago but it's always fascinating how much more information turns up here. I've been contemplating what David said about brightness perception being keyed to bluer wavelengths, and how that may figure into my impressions of different binos.
I'm still somewhat waiting ! lol :-O
Some folks here have made some very good points.
Some of the differences in transmission levels across different wavelengths are indeed design choices (dealt with through AR, and Dielectric, and other coatings), some such as blocking UV light and (near) NUV light are safety features. Other causes are inherent in the different optical material types and how they handle the different wavelengths. How this all plays out for the individual is, well ...... very much an individual thing ! (physiological makeup, gender, age, yellowing of the lenses etc).
Between all of these factors, designers (and marketers !
dance around all of this voodoo to try and give the best view possible for the desired application. As David said, a lot more is known now than in the world war years. (See the 2005 data modification to the Standard for measuring brightness which attributes slightly more of the blue spectrum to the overall result).
https://en.m.wikipedia.org/wiki/Photometry_(optics)
If you have a look at the Schott catalogues you can see that "HT" glass can be ~1.5% higher transmitting in the blue for a category type. Other manufacturers have their own secret sauce equivalents.
https://www.edmundoptics.com.au/resources/application-notes/optics/optical-glass/
As has been touched on, none of these peak sensitivity values are light switch on/off. There's a lot of interplay between the rods and cones (and the different types - S, M, L, or blue, green, red) , as well as environmental conditions, EP's etc.
https://en.m.wikipedia.org/wiki/Photopic_vision
https://en.m.wikipedia.org/wiki/Cone_cell
I like Swarovski's 'flat' transmission curves, and the 'even' Zeiss HT ones too. I think a fairly flat transmission curve is fairly essential to allow unmodified perception of changing light in the landscape.
One of the most memorable and brilliant natural phenomena I have seen (well apart from ancient tree elders that uproot themselves, walk around, and shimmy and shake right in front of you !) was a Red Rainbow. It may have been caused by dust and/or smoke in the atmosphere, but it was all subtle different shades of reddish, peach, vermillion mauve, save for a tiny sliver of teal in the middle. Magnificent !
You just wouldn't be able to fully appreciate the beauty of that and the light changes leading up to and from it without a neutral colour rendition bin. The 'clarity' of 100% internally reflecting prisms also add to the experience.
I'm sure manufacturers could do better if they put all the bits of the pie together, but it's getting to the point of stacking BB's ..... whether you'd notice a huge change or indeed any change at all is debatable.
Not for me though, the Martian red, Sepia, or P** brown shades of some makers ....... let alone green ham ! :-O
Chosun :gh: