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Technology, colour vision, and ageing

In the realm of colour, there are problems that appear in an ageing population that are overlooked by young engineers who design and market electronic equipment. Colour vision changes with age, as does our sensitivity to light levels. For normal, healthy, mature adults, there is a need for higher light intensity than was required as a child; there are more problems with scattered light and glare; a slower response to changing light intensity; considerably worse contrast sensitivity and colour discrimination; and reduced ability to judge distances or focus on small print.

Computer screens have considerable glare for many people, especially with scatter from traces of cataracts or older eyes. Technology to help can be very simple, and I will suggest three options: (i) change the background from bright white to some other shade (e.g. pale green); (ii) wear polarized glasses, as the computer screen light is strongly polarized the glasses will dim the background; (iii) view the screen via a coloured filter (e.g. try transparent tinted wrapping papers). Cutting the range of colours will minimize chromatic blurring in the viewing. Narrow colour filters can also be helpful for some people with conditions such as dyslexia.

One of the fascinating ways we detect changes in our field of view is to use our eye muscles to continuously flick slightly. If we have a fixed gaze, then objects in our initial field of view fade into obscurity within a short time! This need to concentrate on changes is a consequence of survival instincts. Older eye muscles are weaker and the flick speed drops, with a consequent loss of fine detail in changing scenes.

In terms of intensity, a 70-year-old will need three or four times the light level required by a 20-year-old. The changes vary across the spectrum. As with sound, the higher-frequency range decreases the most. For light, this means that our blue sensitivity falls off faster than the red. Roughly, our blue sensitivity is halved between 10 and 20, a further halving by 40, and yet again by 70. This is very unfortunate, as technological advances in semiconductor light sources are impressive, but in applications, the focus has often been on the techniques and new colours, not on the users. Because it is now possible to make blue light— emitting diodes, they are incorporated in a vast range of equipment, from bedside clocks to displays on TVs and radios.

In terms of viewing, the use of blue light is a remarkably inept choice, as for many (not just older people), text is blurred and difficult to read when set into black plastic housing. For older people, information from clocks and displays is often totally lost with blue LED displays. Green is ideal, as it is our most sensitive colour region. We have evolved to respond efficiently to green as it matches the peak colour signal from the light transmitted through the atmosphere from the sun.

The other technological problem on many CD and TV displays is that the controls are embedded in a black plastic background, so have minimal contrast (for any age user). Initially, I assumed this was meant to be a design feature, but now I realize that making plastics can result in uncontrollable amounts of black flecks, so there is a higher failure rate when using, say, white background displays. The obvious mass-production solution is to use black plastic—then the specks do not show. So, overall, the display quality has been undermined by the production technology.

I will make two final comments on how marketing and displays fail to address all the population. The first is that some 10 per cent of Caucasian males are technically colour blind; the second is that perhaps half of older people have some level of cataracts. Colour blindness is actually a misnomer, as it is assessed by pattern recognition with, say, coloured numbers or pictures embedded in a background. For a ‘standard’ eye response, the colour patterns may show a picture or a number such as an 8. For those with a different sensitivity to colour across the spectrum, the pattern recognition will be different; they may fail to see an image or perhaps a 3 instead of an 8.

I am particularly aware of this, as I fail the standard test, but do so because I have a particularly good red response that extends further than the normal. Hence my colour sensitivity is absolutely fine for matching colours and for enjoying colour images. I take pleasure in seeing colour. This may well be the case with many others who are labelled colour blind, so they should not feel deprived. Indeed, we may justifiably feel superior as we have a greater spectral range. For example, when driving in misty conditions, the extended red response offers better clarity, as red light is scattered less than the shorter wavelengths of the blue and the green.

There are some people who genuinely lack the cone structures in the retina that respond to colour, so their world is in black and white. Whilst they lack the pleasure of seeing many colours, they invariably have compensation in that they have more rod-type detectors (which give the black-white contrast). Since these can be 100 times more sensitive than the colour detectors, their overall light sensitivity may well be far superior to the rest of the population.

Cataracts are common. They not only cause image blurring, but strongly absorb light at the blue end of the spectrum, so as the cataracts develop, images progressively move into being more yellow and then red. For anyone who wishes to see how the consequences develop, I recommend looking at websites that display images of the paintings of Monet. He had a small pond and bridge in his garden that he painted over the years. His pictures offer a remarkably accurate description of the development of his cataracts. The fine detail fades into very broad brush strokes and the spectrum progressively moves to the red. Eventually he had the cataracts removed and was horrified by his paintings, but medically they are a brilliant record of cataract problems.

Such subtlety in colour presentation and the corrections needed for it do not yet seem to be appreciated by those generating modern displays, although there is a clear market (unfortunately, many of the displays are not ‘clear’).

 
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