Can you tell red from green?
By Dr Alex Wade, Research Fellow at
(this article appeared in
Planet Medica, April 2000)
The next time you go strawberry picking, imagine how
much harder it would be if the fruit were the same colour
as the leaves. If you are a man, there is a 10% chance that
they are! So is this a problem you need to worry about?
Roughly 1 in 10 men are fully or partly colour blind. This means that one of the three types of colour detectors in their eyes is either faulty or missing altogether.The condition is hereditary and sex-linked: fathers will pass the gene to their daughters (but not their sons) andmothers can pass it to all their children. However, because women can be unaffected carriers, men are at least 20 times more likely than women to develop colour blindness.
Colour blindness is not a particularly serious
condition. Although one type of colour
detector (or cone cell) is missing, the gaps
are filled seamlessly by cones of the other
two sorts. The more important aspects of
vision are rarely affected. People who are
colour blind are, in general, no more likely to
suffer from short- or long-sightedness or to
develop eye diseases such as glaucoma or
cataracts later in life.
The effects of colour blindness are so mild
that many boys only realise that they have
it at a relatively late age. Since they were
born colour blind, the world has always
looked perfectly normal to them. It is only
when they have a sight test at school, or
get into an argument with a friend about
whether something is red or green, that
they find their view of the world does not
always match that of other people.
It is important to remember that people with
colour blindness generally can see most colours;
they just have trouble distinguishing between some
shades of red and green. Apart from making terrible
strawberry pickers, people who are colour
blind are excluded from certain jobs for safety
reasons. For example, they cannot be airline pilots,
policemen or ship captains. Their everyday lives are
also fraught with occasional minor hazards: how to
match socks, how to decide whether the power
indicator on the stereo is red or green, how
to find red golf tees in the grass and how to choose
an appropriate colour scheme for decorating the house.
Clever ways to compensate for colour blindness
If you are colour blind, there are some strategies
that can help. Getting a friend or partner to advise
on matching socks and ties will stop you committing the more
serious fashion crimes, while asking a shop assistan's
advice when buying clothes, paint, carpets and wallpaper
is just common sense. Most colour-blind people learn
at an early age to use clues to help them guess what colour
something might be. Red and green traffic lights might look
similar, but knowing that red is always at
the top can help (although see footnote below).
Often, red and green
things that look alike under fluorescent light will look
different in the daylight. Try taking your ties nearer to
the window in a shop before you decide which one to buy.
On the positive side, there is some evidence that
colour-blind people are much better than average at
certain jobs. They are very good at finding green things
hidden against green backgrounds - for example grass or
leaves. They tend to find things by shape and get less
confused by camouflage. Because of this, colour-blind
entomologists still catch lots of bugs and in wartime,
armies prize their colour-blind snipers and spotters.
So, if you are colour blind and have trouble picking
strawberries, why not try your hand at green beans or
peas instead? You might be surprised at how well you do!
One of our readers took issue with the traffic light idea:
I found your site very interesting. However I would like to
disagree with you regarding your example of the red traffic light.
The spectrum of the red light is predominantly red and being moderatly
colourblind for red I find the intensity of the red light diminished.
If I am a distance away from the light the amplitude of light is to low
for me to see at all and thus can't determine if it is the top, middle
or bottom light burning. There just are no light! As I get closer to
the light the intensity increases and I start to see the red light.
To compensate I watch the other vehicles ahead and on my side and if
they start to reduce speed I know there must be a red light ahead.
Bear in mind that light intensity decreases by the square of the distance.
That is if you double the distance from the light source you only get a
quarter of the light.
* Thanks to Roman Molas for pointing out that these are mock strawberries