This is the first
article of a short series that is intended to describe and document how
bee-colours are simulated by the author and why:
As humans we are used
to see the world in colours rather than in black, white and grey. However,
seeing colours is only possible because there are special cells in our retina,
so called cone-cells that exist in three different types. One type is capable of absorbing mainly blue light (S), a second
one absorbs mainly green (M) and the third type (L) absorbs red light (fig. 1).
Figure 1: Absorption of light colours (wavelengths) in the three different human
cone-cells. (http://commons.wikimedia.org/wiki/File:Cone-response.svg#filelinks)
The colours that the human
eye can see can be displayed in the RGB colour space, which is composed of the
three basic colours red, green and blue. If three light-rays of the basic
colours are pointed on a screen, the intersection of the three appears white. As
soon as one of the three colours is missing, we see a colour that is composed
of the remaining two (fig. 2).
Figure 2: Composition of the colour white and the results when two of the basic
colours are mixed.
All the additional
shades of each colour that our eyes can distinguish are achieved by combining
the basic colours in different intensities (saturation) and different
luminosities.
The eyes of bees and
humans are quite different. Additionally, the nervous systems that have to deal
with the information that is captured by the eyes are even more different in
size and structure.
However, there is one
important thing that both organisms have in common: Bees and humans both have
three different light sensitive pigments with absorption maxima distinct from
each other. (Both are trichromatic organisms).
If we look at the
light spectrum that a bee can see with our eyes, we can see only a fraction of
it. For the sake of simplicity one can assume that bees eyes are sensitive for
near UV (below 400 nm) but cannot see the light that appears red to humans on
the other end of the spectrum. This is illustrated in fig. 3:
Red disappears,
because bees have no receptor for this part of the spectrum. Instead, they see
ultraviolet (UV). Since the latter is invisible to the human eye it is show as
black (fig. 3).
Figure 3: The spectrum
visible to bees as seen with the human eye.
In order to get an
approximate visualisation of the entire spectrum that a bee can see we will use
a trick (simulation): We will move „our“ colours in the spectrum that the bee’s
eyes can detect. This means that ultraviolet becomes bee-blue, blue becomes
bee-green and green becomes bee-red (fig. 4).
Figure 4: The
spectrum visible to bees moved into the human colour-space.
It is not intended to
postulate that bees do indeed see the colours as shown here. It is just an
approximation to simulate how a trichromatic vision with a shifted spectrum
could look like and how the UV reflection / signature of flowers contribute to
the overall appearance considering the entire spectrum visible to the
pollinators.
Image references:
Fig. 2-4: Copyright,
Nicolas Chalwatzis, 2013
