Busting the Fluorescence Myth

OK, let's get real.

First, what is fluorescence?

From dictionary.com: "the emission of radiation, esp. of visible light, by a substance during exposure to external radiation, as light or x-rays."

Fluorescence is different than reflection, which is the light by which we see most things. Reflected light is always the same wavelength before as after reflection, if no refraction is involved.

Fluorescence is light generated by an object's surface as a result of the power of the light stimulating the response, but not usually of the same wavelength. Think of the bright glow from your white shirt when under black (UV) lights. The shirt's pigments are stimulated by the UV light, and emit visible (apparently "white") light, even though there are no white lights in the room. Looks kinda magical, no? Many materials/pigments have fluorescent properties, but most are so low in intensity that detection is not possible in processing environments.

Key Technology's "color" sorters have been sorting green peas using fluorescence for more 12 years. Peas (as well as any green seed from the interior of a green pod, like the seeds of string beans) glow bright red under UV light, and even brighter after they are blanched. This is a typical property of chlorophyll, the substance that makes vegetables green. Such a property makes it easy for a "color" sorter to remove everything that is not a good green pea: 1) Make sure that no external red light shines of the product, so the only red light will be fluorescence from good peas; 2) Shine UV light on the peas; 3) Everything that is bright red is a good pea; everything that is not bright red is not a pea, sort it out.

Makes for a nearly perfect sort.

Now take a peek at potatoes. The most common source of fluorescence is again from chlorophyll, from the greening that occurs when potatoes get exposed to sunlight. Laser systems can focus a high concentration of energy on green areas to make them glow quite brightly and so make them distinguishable from.... white potato flesh.

Just like trichromatic cameras have done for years. And all the systems in place for quality control of cut potato products prior to blanching employ cameras.

So what is the benefit of fluorescence in potato applications? None useful, to date. Now, it may be possible to identify some potato fluorescence other than that caused by chlorophyll. Perhaps we will find such a phenomenon where everything that is potato glows one color and everything that is not potato fails to glow in that color.

Until then, we will use cameras for the best possible quality control in cut potato products.

Next time, we will discuss laser applications: Where in a potato plant would you employ lasers?

Tim

Stumble It!

Bookmark on del.icio.us