Adrian Posted March 12, 2019 Share Posted March 12, 2019 I have been photographing various plants with IR luminescence recently, and this one is the first to show definite differences between the visible and IR luminescent image. The plant is a cultivated Heucherella "Twilight" Technical details for IR: Nikon D300 with 105mm Series E lens. IR 850nm filter.Light source: LEDWAVE Wild Finder torch 490 - 520nm emitting, peaking at 505nm Link to comment
Guest Posted March 12, 2019 Share Posted March 12, 2019 Hi Adrian, Have you tested the torch used here for IR emission as well? When I shoot my IR fluorescence images I always get an uneasy feeling that my source/illumination is contaminating my subject with IR - thus yielding something of a combination IR reflectance/fluorescence image. So, I'm always second guessing my IR fluorescence images - probably because I can't see the image in the first place! Link to comment
Adrian Posted March 13, 2019 Author Share Posted March 13, 2019 MarkI have tried a whole variety of subjects over the last few days: fossils, paintings, flowers, leaves etc.With those subjects showing no luminescence, the frame is completely black, so I can only assume that there is no residual IR from the torch.I will try to find a graph for the output of the LED. Link to comment
Andy Perrin Posted March 14, 2019 Share Posted March 14, 2019 Just on physical grounds, there isn't any obvious reason that I can see why an LED would emit that far out of band? The light is coming from when the electrons jump from the conduction band to the valence band, which are separated by a energy gap of a certain amount that is fixed by the identity of the semiconductor material. That bandgap controls the color of the resulting light, which is why it's so nearly monochromatic. Link to comment
ulf Posted March 14, 2019 Share Posted March 14, 2019 Just on physical grounds, there isn't any obvious reason that I can see why an LED would emit that far out of band? The light is coming from when the electrons jump from the conduction band to the valence band, which are separated by a energy gap of a certain amount that is fixed by the identity of the semiconductor material. That bandgap controls the color of the resulting light, which is why it's so nearly monochromatic.That is how it works. There might still be something in or around the torch that have fluorescence, that needs to be filtered. The half width of most LEDs are often in the range of 12-16nm.I have a green 525nm LED that deviates with a width of 33nm. Link to comment
Andrea B. Posted March 15, 2019 Share Posted March 15, 2019 So this is Visibly-induced Infrared Fluorescence? Or VIIF?*Very* interesting! I'm also wondering what pigments are in the periphery of those Heuchera leaves? I have some rather tiny little Green and Cyan LED mini-torches. I must add an experiment to my list to try these for IR fluorescence. Link to comment
Adrian Posted March 18, 2019 Author Share Posted March 18, 2019 Andrea,I have always been told that, because it is "invisible", we do not know if the effect persists after the light source has been removed, that it should be called luminescence rather than fluorescence.All of the references I have found to it recommend a cyan light source.Adrian Link to comment
Andrea B. Posted March 28, 2019 Share Posted March 28, 2019 Perhaps use video to determine whether you have phosphorescence or fluorescence. :D Link to comment
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