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http://www.ultraviol...-bee-colours-i/
This is the first article of a short series that is intended to describe and document how false colours are used by the author to visualise the colour spectrum that bees and other insects can see. This colour spectrum is referred to as "bee-colours".
(Comment: The nomenclature for the false colours used to simulate the colour spectrum visible to bees and other insects has been modified, since it turned out that the initial approach was confusing for people who are familiar with a different use in the literature)
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. (source: http://commons.wikim...e.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: Colour spectrum visible to humans and the resulting colour if two or three of the basic colours are reflected from the same surface.
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:
Deep red is invisible to bees (black), 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). The figure also illustrates that the colours blue, green and cyan look the same for human eyes regardless if they are combined with UV or not.
Figure 3: The spectrum visible to bees as seen with the human eye. Since we have no receptor for UV in our eyes, we can only detect the remaining two colours.
In order to get an approximate visualisation of the entire spectrum that a bee can see we will use a trick (simulation): We will map false-colours to the entire spectrum that bees can see: In the approach used here ultraviolet is visualised as “false-blue”, blue is shown as “false-green” and green is represented by “false-red” (fig. 4). Now we have assigned a false-colour to every colour that a bee's eye can detect. The effect of combining the three main bee-colours with each other is also visualized.
Figure 4: The spectrum visible to bees represented by false-colours.
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 different 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. By using all existing colours as false-colours we can simulate more colour shades than we could with an approach that leaves out a part of the colour space.
Another way to illustrate the mapping of the false-colours is shown in fig. 5. However, this figure does not illustrate the mapping of false-magenta to a colour composed of UV + green.
Figure 5: False colour mapping used to visualize the spectrum visible to bees.
Image references:
Fig. 1 from: http://commons.wikim...e.svg#filelinks
Fig. 2-5: Copyright, Nicolas Chalwatzis, 2013
Published 27 December 2013
Major modifications concerning false-colour nomenclature 4 January 2014
