I wondered around in my home with my mobile UV LED Lamp in my hands, my UV stopping googles on in search of some unusual effects this strong 365nm UV light might show. A primula plant I just bought catched my attention, since while I was lighting the flowers (the "usual suspects" so to speak...], UV light also fell onto the deep green leaves of that beautiful plant. And to my big surprise, I saw them lighten up in a mysteriously dark glowing red!
I grabbed my camera and took some shots of that effect, using a suitable macro lens (X35) and a UV Cut filter - more about that later, since it turned out to be a nontrivial issue....
So this is how that plant looked in visible light, well known to most of us: [as usual, a click on an image opens up a larger view]
Switching from visible light to UV light, using my 365nm Nichia UV LED flash/lamp, the scene dramatically changes and that deep red lights up from the green leaves! I used an UV stopping filter in front of the lens, in this case the 2" Baader UV/IR Cut filter.
To record that emitted red light in a picture turned out to be nontrivial, since most cut filters I have here also cut off that red light and I just got a grey or greenish color. The spectrometer reveals why this is the case, it starts at about 650nm and extends into the near IR (NIR) region, most of these filter cut off. The only one which worked somewhat was the Baader UV/IR Cut filter. The Canon, Tiffen etc. UV/IR cut filters ("hot mirror") all failed since they are designed to cut off NIR.
But what is that what we see here? It is UV stimulated near infrared (NIR) fluorescence of the green chlorophyll (which is a type of porphyrine we have seen in the egg study I published earlier)!
So I hope you enjoyed that "hidden beauty" of that Primula flower!
Stay tuned, more will follow on that fascinating subject...
More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos
