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Just like a ripple in the pond -- light, as well -- is a waveform. So, too, is sound. And all are bound by the very same laws of physics. Consider red ... This could be represented by a medium-sized stone being tossed into the pond. The resulting wave propagating around the point of impact will reveal a repetitive pattern of evenly spaced waveforms. Now, switch to a smaller stone. This could represent the color blue, with a shorter wavelength, resulting in a repetitive pattern where the wavefronts are more closely spaced. But drop both of the above stones next to one another -- in close proximity -- and, where the two wavefronts meets, the original waves will break up, as well as reduce in amplitude (the peak wave crests will be reduced).

As it relates to sound, the above anomaly is to the frustrating chagrin of the audio engineer designing a multi-element loudspeaker system ... to the Acoustician endeavoring to tune a concert hall. In this aural world, the phenomenon is known as 'Phase Cancellation' -- where one waveform, meeting yet another, results in varying degrees of cancellation between two or more waves. To compound the problem, other 'phantom' waves emerge with this interaction, serving up waves that were never intended ... or desired.

And, in light, the scientific community refers to the very same interaction as 'Destructive Interference'. Here, too, it occurs when different wavelengths (often measured in nanometers) collide and mix -- even those within what may be regarded as the same 'Color Name Family' -- such as 'Red' and 'Infra-Red'. You could just as easily call these two wavelengths 'Cat' and 'Dog' -- it would matter, not. And, moreover, a third -- undesired -- wavelength would be "constructed" as the sum difference between the two wavefronts, while the original two waves would be suppressed. This, the chief reason that DermaWave heads do not combine different LEDs in the same head -- including the often misguided mix of Red with Infrared.

But don't simply take our word for it ... Given that the Photo Rejuvenation industry seems to be so fond of citing 'NASA Research', endeavoring to associate themselves with the same, let's look at a demonstration graphic provided to us by NASA, themselves ...

 

NASA's use of 'Red and 'Blue' waves represents arbitrary color-coding to reflect two different light waves of any color - or wavelength. Let it be said that, for complete cancellation, the two wavelengths would need to have a precise mathematical relationship to one another, but interference and cancellation will always occur with any two -- or more -- wavelengths.


Many distributors cite NASA as using three wavelengths relating to their research concerning cell regeneration. What they don't tell you -- and likely don't even know, themselves -- is that NASA never used any two - or three - wavelengths at once, at any given time. After all, as NASA's own graphic demonstrates, they knew better -- as would your high school science teacher. And further, the NASA 'Destructive Interference' graphic covers only that ... destruction of the two waveforms. What it doesn't show you is what also ensues when two wavelengths are placed in close proximity to one another and mixed. A new waveform - (wavelength or color) is now created, with the original two being suppressed ...

Hare some other sources that will express the above in even more scientific terms (but still having some element of fun). We'll also be providing them at the end if this article, should you wish to continue with your reading ...

Excellent Interactive Java module links, demonstrating Destructive Interference:
 

 

DESTRUCTIVE INTERFERENCE DISPLAY from OLYMPUS OPTICAL Very nicely done, from the Scientific Division of Olympus Camera DESTRUCTIVE INTERFERENCE DISPLAY from FLORIDA STATE UNIVERSITY Extremely similar to the Olympus Interactive Java, but some of you may like this one a little better.

Anyway, you may be wondering, does this indeed apply to those heads that combine Red LEDs (around 660nm) with Infrared emitters (around 940nm) -- those originally designed as low-level pain relief devices, or misguided copies of the same? Oh, yes, indeed. With the LEDs generally placed closer than 1cm apart, combined with the typical projection angle of an LED -- about 20 degrees, the two waveforms most definitely combine and mix, resulting in near full-blown destructive interference. And even if they used a very tight, 5 degree projection angle (not common), the light scatters violently to the sides as soon as it strikes the skin surface, essentially interacting in any event.

Case in point: We took one of those aluminum heads that employed both 660nm (basic red) and 950nm (infrared) LEDs in the same unit and "masked out" the infrared LEDs with black, heat-shrinkable tubing. Once we did so, the output of the neighboring 660nm emitters, measured with a Spectrometer, went up over three-fold. That's how significant destructive interference can be. To put it in colloquial terms, it proved to be the head design that screwed itself.

Is there a work-around for this? Kind of. Sort of. But not necessarily a satisfactory one ... Given the use of a pulsed circuit, one could design a head that 'toggled' back and forth, between the two wavelengths -- whereby, as one wavelength pulsed 'On', the other wavelength would pulse 'Off', back and forth, where the two would never "meet". BUT ... to do so would limit the circuit to a 50% Duty Cycle, whereby both wavelengths would be inactive half of the time, greatly increasing the 'time to effectiveness ratio' (which isn't a good thing).

One maker of an inexpensive, all-in-one LED head unit - The Quasar SP - endeavored to run four wavelengths within their head (marketing running amok), sequentially pulsing the four -- one after the other -- to eliminate the "harmonics" (that which more commonly relates to sound, actually, but their term for Destructive Interference). Now, to do that, each LED could only be on 25% of the time, profoundly reducing efficiency.

But even if you we willing to put up with this loss of efficiency, there still remains another problem. By toggling spaced LEDs on and off, as described above, the coverage for any one wavelenth becomes very spotty, with each 'On' LED being "space interrupted" by the LEDs that are in their off state. So even more efficiency is lost ... in two ways, for a total of a '1/16th efficency loss'. Not good. And all of this for a cluster of LEDs that have never been recoginized by the FDA for the stated application.

For those who simply re-labeled a low-level Pain Relief machine as a Photo Rejuvenation device -- or the others who made the mistake of copying the same -- we suppose that they're stuck with what they contracted for distributorship. But YOU don't have to be ...

And here are some independent source links that will tell you the very same thing your high school science teacher would ... just like we've been telling you all along ...

DESTRUCTIVE INTERFERENCE DISPLAY from OLYMPUS OPTICAL   DESTRUCTIVE INTERFERENCE DISPLAY from FLORIDA STATE UNIVERSITY   DESTRUCTIVE INTERFERENCE from SCIENCE WORLD'S 'LAW OF PHYSICS'