Colour vision test: annually, or once per lifetime? (and colour vision discussion)

Malibuflyer wrote:

People with this form of color blindness have difficulties differentiating blue and yellow – not blue and green.

Where have you heard this? In Norwegian it’s called (translated) “blue blind”. This is still not clinically “correct”, but closer because it’s the diminished/lack of picking up high frequency color (ie in the blue spectrum) that is the problem, damaged or lack of S cones cells.

From google:

Tritan-type color vision is characterized by a loss of color discrimination for shades of blue and yellow. Tritanomaly, causing reduced blue sensitivity and Tritanopia, resulting in no blue sensitivity, can be inherited or acquired; the inherited form is a rare autosomal recessive condition. More commonly, tritanomaly is acquired later in life due to age-related or environmental factors. Cataracts, glaucoma and age related macular degeneration could cause someone to test as a Tritan. People with tritanomaly have reduced sensitivity in their blue “S” cone cells, which can cause confusion between blue versus green and red from purple. If you believe you have tritanomaly, we recommend you consult with an eye care professional for a complete vision assessment.

For me it is hard to impossible to distinguish red from purple (depending on the exact colors used in tests). I have no problems distinguishing blue from green, but when looking at blue or green independently, it is almost impossible to say if this is blue or green, depending on light source and light intensity (and I guess the exact shade of blue or green). It’s not an on/off digital kind of thing, but very analog and fuzzy. I don’t have tritanopia, but some kind of tritanomaly.

Malibuflyer wrote:

Color blindness medically is not at all associated with the inability to “correctly” (in the sense of majority consensus) name a color when looking at it. It is always of if you can tell two colors apart if you se them next to each other (in the sense of saying “these are two different colors”)

Colors are fascinating stuff. It’s rather complex when mixed, but it’s all easily measurable. It’s just a mix of different (visual) frequencies of light. All color blindness are some form of loss of function (small to total) of one or more of the 3 types of cone cells in the retina that detect color. This will cause problems seeing certain colors and/or problems distinguishing between certain colors. Now, tests are almost exclusively made to distinguish colors, simply because the answer will then be independent of the absolute perception of color. The answer is “4” or a point in an area for instance, ie right or wrong.

Peter wrote:

And it’s stupid because CV rarely varies over a lifetime

It can, but the most common form that the Ishara test tests for, is usually (99.9 prob) a genetic defect that you are born with.

LeSving wrote:

It’s rather complex when mixed, but it’s all easily measurable. It’s just a mix of different (visual) frequencies of light.

Not really. For any given colour that can be observed by a “normal” human, there an infinite number of different spectral distributions that will look the same. i.e. that hue will stimulate the cones in exactly the same way. This phenomenon is called metamerism. This is also why two patches can match exactly under say daylight i.e. they look the same but with different spectral distributions, that will then look different to each other under different lighting as this matching pattern deviates under the new light. This can happens with lighting from an LED which often covers very narrow parts of the spectrum. This is why you don’t want to match your aircraft’s paintwork using paint tinted with just 3 or 4 colours…
This also applies to white lights, for example a “daylight” LED has a completely different visible spectrum to real daylight, a tungsten matched LED is different to standard incandescent light bulb etc.

Is that because all light haa different colour temperatures? In photography some photographers regularly use colour temperature meters.
But light also changes depending texture and the nap of the material that gives that texture. You can see that on carpets or lawns after they have been cut.
Nearly everything we see is down to reflective light and there are a number of different things which can change that reflected light, just look at the sea.
But none of this affects the CV test we do at the AME which embeds a different colour in a background of colours so it stands out as a number. If it doesn’t your brain has a problem recognising that particular colour.
But it is not about recognising a particular hue.
Very few people can identify similar but different colour hues. Eg Cyan and turquoise, one is a shade of blue and the other, some identify as a shade of green.
Then you have the difference between a darker shade of yellow (sun) and orange. On the colour wheel some of these are incredibly close, some though come from the other end of the spectrum especially where very dark reds and purples are concerned.

gallois wrote:

Is that because all light haa different colour temperatures?

Colour temperature is just a scale like Celsius or metres. It is ideally something very hot at the temperature given, like the sun. If you heat a black body to something around 5000K it will look like daylight, and radiate a spectrum very similar to the sun. If you use a cheap LED that is designed to match 5K it can be a match for a “normal” human but it will have completely different spectrum possibly two or three large peaks, the spectral peaks of the light will such that it matches the spectral peaks of normal human eyes in such a way that you can’t tell the difference. If you use a digital camera or old film camera which WILL have a different spectral sensitivity it will be able to see a difference when a human can’t and vis versa. This is sometimes called metamerism failure or the like. You can buy better LED lights that are better spectral match for critical colour work, even if they are same colour.

Ishara tests would be printed using carefully chosen inks and should be observed with the correct broad spectrum light, which at a guess is probably daylight. So ishara tests generated by a computer display are not the same, even if the colours look the same…

Ted wrote:

For any given colour that can be observed by a “normal” human, there an infinite number of different spectral distributions that will look the same. i.e. that hue will stimulate the cones in exactly the same way. This phenomenon is called metamerism.

Even more interestingly, there are people with four kinds of cone cells. They can see colours that ordinary people can’t. (Or, to be precise, they can percieve as different two colours that look exactly the same to a person with “normal” colour vision.)

This is also why two patches can match exactly under say daylight i.e. they look the same but with different spectral distributions, that will then look different to each other under different lighting as this matching pattern deviates under the new light

I know. IMO this is due to the absorption spectrum of the pigments vs the frequency spectrum of the light source. Light intensity also play a part I would think. In the night, all cats are gray, but other animals have evolved to see perfectly in the night.

But also the brain translates different colour temperatures. Eg.The fluorescent lights you get in a supermarket give everything a green hue.
This is different to the difference between daylight and artificial light (or an added change)
So old movie film had the.colour temperature range marked on it but it was also marked daylight or artificial film. However, although your eye will see that green hue of the fluorescent light in the supermarket, the brain translates this into something it expects and it just looks light normal artificial lighting. It’s a bit like when you use the white balance on a digital camera you can fool the sensors into seeing.white where the hue is actually green. Once the scene.becomes an image the brain does not interpret/translate the hues, it sees what it sees.

That’s a different effect, yes the brain does adapt to different colour temperature of the light source. Tungsten and daylight are both broad spectrum light sources, Fluorescents and cheap LEDs have the additional problem of very narrow spectral distributions with peaks that do not occur in daylight or tungsten. This is a problem for film or digital in critical colour work. Because the camera will see these peaks differently to the human eye. If you use a cheap light you may be able match a colour in a t shirt but the rest will not match correctly.

Motion picture used to typically use tungsten film outdoors with a balance filter, this worked well because daylight and tungsten are broad spectrum. This technique won’t work properly with a florescent or cheap LED. In the case of digital it can use 3d matrix to translate these type of errors, which is part and parcel of how a digital camera works, but to do it properly you need a reference taken in the correct broad spectrum light to correct the errors, but it will never be perfect if the light is particularly bad.

Yes we used to use various tungsten filters, but the top cameramen were always aware of colour temperatures where they would know ho to correct to get the result they wanted at the laboratory. David Watkins, Dougie Slocombe , Vittorio Storaro and many others designed their own lights to deal with the colour correction and to match sunlight. They always knew what the different colour temperatures would do on the film they were using, and how to use it for the effect they wanted. With digital we used to tweak the white balance, as I wrote, to balance the colour temps. The tungsten v daylight filter was to take out the blue that would.occur if you shot daylight with tungsten film. But you only did that when you weren’t able to go with 2 types of film (unless the work called for it)
Much as I love discussing film and photography this has nothing to do with doing a CV test at.an AME.where you have a book of printed sheets, where a number or symbol should stand out . The number or symbol should always stand out, whatever the lighting conditions (save dark conditions as colour tends to disappear the darker it gets) . The brain does not try to translate because it has nothing to base its translation on so takes everything as is. What this means, if I understand LeSving correctly is that he can see the number but he couldn’t tell you whether the background was blue and the number was green.

gallois wrote:

Much as I love discussing film and photography this has nothing to do with doing a CV test at.an AME.

What we are discussing is really about metamerism which is really part of the fundamentals, the Physics in fact! A chemist may not have to worry about sub atomic particles but it is still relevant…

gallois wrote:

The number or symbol should always stand out, whatever the lighting conditions