[lcedp]

Doesn't seem very legit to me.

Firstly, if wi-fi would be visible, you still wouldn't be able to see it all like we can't see visible laser ray unless there is dust/water/something in the air. It should be reflected from something to be seen.

But let's suppose it's just visible per se.. Ok, colors represent waves, but they don't look like 3-5 inches, more like meters on some photos.

Secondly, signal strength should dramatically decrease over distance. In two meters it should be four times as dark as in one meter, in 10 meters it should be 100 times darker.

Thirdly, on many pictures waves don't seem to disperse properly. Looks like everybody's using a very advance ridiculously narrow-range antennas.

[VLM]

"signal strength should dramatically decrease over distance."

One of the very few things they got right from a physics perspective is your eyes respond vaguely logarithmically. Its supposedly not really, deep in the decimal points theres a buried power law factor and a buried linear factor at low levels, but close enough to log for all astronomical purposes. They worked with an astro-biologist per the article; I assume this is the "astro-" portion contribution.

Google for astronomical magnitude and there's also some interesting quantitative chemical analysis stuff having to do with light adsorption. In my misbegotten youth I spent a lot of time in a chem lab squirting weird stuff into sample tubes and hovering over an ancient spectrophotometer. A spectrophotometer is kind of like what an EE would call a RF network analyzer, but for light waves, sort of. At least that's the best EE analogy I can come up with. Eventually I spent most of my lab time daydreaming about getting home to play with electronics and computers; why was I trying to become a chemist? It was pretty interesting stuff to experience in retrospect.

The visibility is... questionable. Google for "clear air return" and WSR-88d and stuff like that. A "decent" wx radar is sensitive enough to get at least some return from turbulence. How do you know its not just ground clutter? Because the doppler shift matches the direction and speed (more or less) of ground instruments. The questionable bit is clear air return is a bazzilion dB reflection loss below actual real reflectors so it would be incredibly faint compared to actual reflectors.

Also the humorous artistic waves don't show multipath like real waves. Not unusual in an urban environment to end up multipath limited not raw sig strength limited, at least in other applications; donno if wifi is usually limited like that.

[sp332]

"In two meters it should be four times as dark as in one meter"

But our eyes compensate for inverse square laws, and have a logarithmic response to light.

[lcedp]

Ok, point taken. It is vaguely a logarithm function. But what's the base of this logarithm? How much is it curved?

Just try light up a big room which has no windows with a candle - you can see pretty well at the distance of your hand, but in a few meters from you - it's plain darkness. I expect wi-fi waves to be like this.

Using the grath "Perceived Brightness" at [1] we have roughly the following table:

    Distance/Actual/Perceived Brightness
    1/100/100
    2/25/~55
    4/6.25/~30

[1] http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.htm...

[sp332]

Luminous efficacy depends on wavelength, with the eye being most sensitive to 555nm (green) light at 683 lumens/Watt. Most wifi setups max out at 1W (I think?), so if the eye were as sensitive to wifi signals as to green light, we could get 683 lumens which is about the same as a 60W incandescent bulb.

[lcedp]

And?

[sp332]

Oh, so if we're trying to imagine how bright a wifi router's "light output" would look if we could see it, we can just imagine a 60W (monchromatic, say green) lightbulb. Of course the light would pass through walls more easily which is a bit unusual :) But for attenuation over free space, I think the analogy to a 60W light bulb is very useful.