Cuttlefish colour changes inspire new energy-efficient TV screen design
by Jonathan Sarfati
Published: 21 May 2009(GMT+10)
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Cuttlefish are well known for their brilliant colour changes, and are even known
as the “chameleons of the sea”. Sometimes they produce a zebra stripe
pattern that even appears to move across the body. They have several ways of doing
this, and one of them has inspired scientists to design a new type of TV screen,
with very low power requirements—under 1% of normal screens.
How cuttlefish change colour1
Cuttlefish have several types of structures that allow it to change colour rapidly
Chromatophore
This is a group of cells that include an elastic saccule that holds a pigment, plus
15–25 muscles attached to this saccule. When the muscle contracts, it stretches
the saccule so it covers a wider area. Chameleon colour2 is also largely caused by chromatophores, but cuttlefish
chromatophores each have a nerve ending. This allows finer control, so one saccule
can be expanded while the neighbouring ones contract. This allows the cuttlefish
to produce complex patterns that can change quickly.
Iridophore
These are tiny stacks of plates, which act as a diffraction grating, and produce
iridescent colours. Iridescent blues in butterflies and birds are also produced
by diffraction, i.e. splitting and spreading out the different colours
of the spectrum. Depending on the spacing and the angle of the observer, different
colours are seen. These are called structural colours, since they depend
on the structure of the material rather than a pigment. In the cuttlefish, iridophore
colours are relatively fixed, but hormones do cause some change.
Leucophore
These are similar to iridophores, but are flat and more orderly plates that reflect
light rather than diffract it. Their colour matches the surrounding light: white
light will produce a white shine, but if incoming light is a different colour, then
that’s what will be reflected. This helps with camouflage.
Photophore
This actually emits light, rather than absorb (pigment), diffract (iridophore)
or reflect (leucophore) already existing light. They use bioluminescence,
or producing light from a chemical reaction with very little heat. Sometimes, these
creatures have sacs containing bioluminescent bacteria in a symbiotic relationship.
New TV screen design
A team led by Edwin Thomas at the Massachusetts Institute of Technology knows a
good technology when they see it, and described it in the journal Advanced Materials.
Dr Thomas explains, evidently talking about the iridophores:
Cuttlefish change their color by secreting different chemicals to change the spacing
between membranes. … We have created an artificial electrical system to control
the spacing between layers.3
The prototype screen is a few inches square, but only a micron thick (a thousandth
of a millimetre). Filling this micron are very thin layers of alternating “dirt
cheap polystyrene” with poly(2-vinylpyridine) (2VP). The former is inert, but the latter expands when a small voltage is applied. By increasing the voltage, the 2VP layer thickness increases, and with it the light wavelength reflected to the viewer.4 So
low voltage produces violet and blue light while higher voltages move through the
spectrum until red is seen at 10 V.
The tunability of these systems is fantastic. There is a huge span of colors and
applications.—Stephen Foulger
The screen doesn’t emit light, which is why it needs very low power. But this
means it needs an external light source shining on it. And it needs to be viewed
from right in front, because the image colour changes with angle.
According to Thomas, it’s very easy to assembly such a screen. So he is working
with a local high school science teacher to make a variety that is simple, cheap
and safe enough for schoolchildren to build in a chemistry class. But despite its
simplicity, Stephen Foulger, of Clemson University, South Carolina, says:
The tunability of these systems is fantastic. There is a huge span of colors and
applications.
This is hardly the first time that Nature—or rather, the Designer
of Nature—has surprised scientists with sophisticated and efficient ways of
producing exquisite colours and patterns (see articles below5).6
Related articles
Further reading
Related resources
References
- James Wood and Kelsie Jackson,
How Cephalopods Change Color, Bermuda Biological Station for Research,
16 September 2004. Naturally this paper gives a fact-free homage to evolution, but
it has good design information. Return to text.
- See also By Design, 2008 (above), ch. 3: Colours and
patterns. Return to text.
- Eric Bland,
Color-shifting cuttlefish inspire TV screens: Prototype uses less than one-hundredth
the power of traditional displays, <MSNBC.com>, 12 May 2009.
Return to text.
- Reporting on Dr Thomas’ earlier research on the same lines, the article Gel Changes Color on Demand explains, “The key to manipulating the thickness of the poly–2-vinyl-pyridine (2VP) layer is to give the nitrogens on each segment of the 2VP block a positive charge, yielding a polyelectrolyte chain that can swell to more than 1,000 percent its volume in water.”Return to text.
- See also By Design, 2008 (above), ch. 3: Colours and
patterns. Return to text.
- I was first alerted to this new biomimetics example in Cuttlefish Inspire Reflective Screens,
Creation-Evolution Headlines, <creationsafaris.com>, 20 April 2009.
Return to text.
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