Article Category: Digital Signage | Article Tags: chemistry, digital signage, LED, price trends
I was filling my gas tank on a rainy morning at a local Shell station. Each pump comes with a piece of digital signage (a video screen) that loops commercials and things. Since the rain had been coming down in wind, the screen was covered in water, and there was a slight rainbow effect coming from each speckle of water [I snapped a picture of if with my iPhone, which is pictured above]. It instantly took me back to my days as a student in college in my analytical chemistry class, senior year.
Our professor was discussing light emitting diodes, and she matter-of-factually said “…yes, and if you have TV and place a drop of water on your tv screen, you’ll notice through the magnification of the droplet that there are three colors: red, green, and blue. This fact, plus some others that I am about to discuss, is actually the explanation for how the cost of LED was once very high, and why the prices are going down.
Here comes some chemistry
The water is acting as a magnifying glass
The water itself isn’t reacting with the screen or anything like that, its simply acting as a magnifying glass. Because the water is comprised of H20 molecules that are all partially charged, they are held together via hydrogen bonding. This means that a droplet of water is squeezing itself together, and because the most energy stable configuration of those molecules is a sphere, they take a round shape, even if the other half of the sphere is mushed against a flat surface. The tight, shrinking behavior of the droplet is due to surface tension, bonding, and polarization. That round shape is essentially an exaggerated version of what would normally be the lens in a pair of your reading glasses. Imagine if your lenses were spherical! Yikes. The figure to the right actually shows the partially spherical shape as water droplets are mashed against a flat surface.
Under magnification, we see that there are three colors
Yes. There are three colors, and they never change. So the question is how are a grid of pixels containing only three colors able to look like an image on a screen when there are obviously many colors in a picture of your favorite actor or actress? The answer lies in their relative intensity. If you have three lights, one red, one green, and one blue, and you crank up the intensity of the red and blue, and turn down that of the green, you’ll see purplish colors. Shrink that down to the size of a little teeny tiny pixel, and multiply that by about 5 million. That’s a nice little LED TV you’ve got there.
Consider wavelengths of these colors
Now, you may not have a chart of the visible light spectrum handy, but you should know that the color red is a low wavelength, which means that its not very bright. Green and blue, on the other hand, have higher wavelengths and tend to be a bit brighter.
In terms of industry, the cost of production of each LED color is not equal
Some LEDs are very cheap to produce but the LEDs with lower wavelength are less efficient and naturally produce less light, and are consequently more expensive to create. While scientists work on developing more intense, and more importantly, cheaper methods of producing those inefficient LEDs, the price is slowllllly going down. In the beginning, those LED screens were really expensive mostly because of the one expensive LED color.
Presumably, scientists have found a way
Since the prices have gone down, one could logically conclude that they’ve found a smarter and more cost-effective method of producing a more intense light emitting diode for the red LEDs. In fact, any business economics student can tell you about Hoitz Law, which when applied to light emitting diodes, predicts the steady increase of light output of an LED over a span of production years.
This is actually the case with many technologies, and is a decent explanation for why some hardware gets cheaper as time goes on. Its not that the product has become less “new”, its that its getting less expensive to produce. The graph to the right depicts light output vs production year on a logarithmic scale.
Four-color pixels
I’ve even heard of newer TVs having 4 colors in each pixel, and it would probably cause a more saturated and colorful look. But that’s just an educated guess and I’m not sure where I heard that.
Conclusions & the pricing trend with LED technology
In the future, you should expect the cost of LED TV technology to continuously fall. And in consideration of that assumption, I think you can safely consider decorating your business or office with a nice LED TV screen for active marketing and other informational purposes. Digital signage hardware costs are bound to go down over time, and more people will be able to experience their benefits.
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