Hot or Cold? Are all UV sources the same?

I was recently invited to visit my friend Phil Smith up at Lesco UV in Torrance.  Phil told me that they had something new that I needed to see.  Apparently they have developed a new LED system utilizing standard light guides.  I have not been a fan of LED systems because they produce low irradiance (measured in Watts per square inch in the relevant spectrum), a narrow spectral output (or inappropriate spectral output for most of my UV adhesives) and a very small curing area.  However, the guys at Lesco UV insisted they had something better so I checked it out...

My first test was to see what the output was in the UV spectrum.  Using an EIT radiometer I measured the output with a dual light guide and found it to be over 4W/cmsq.  Pretty impressive on a 3mm dual guide, but does it cure my adhesives?  Yes.  While I did not have time to test and compare cured properties, I did find that all of the USB Class VI medical grade adhesives in my EMI Medical Adhesives Sample Kit cured quickly and fully at considerable depths.  My next question was how much heat is produced.

The quick test for this was to compare a Dymax LED system to the Lesco unit with the same output parameters.  I would expect both to produce little thermal build up because LED systems tipically produce a very narrow band of energy.  Now, I can't tell you why  but the Lesco system produced a much "cooler" light than the Dymax unit.  Neither Dymax or my friends at Lesco want to share intimate details of their designs for some reason :(  My suspission is that the Dymax unit uses LEDs that are producing wavelengths that are in the range of 390nm and some energy up in the visible range.  The Lesco unit is focused around 360nm, but again I am speculating at this point.

Check out my simple qualitative side by side test video.  Within seconds, Dymax smoked the black sleeve on this wire while there was almost no thermal build up on the Lesco unit. The UV power measured from the 5mm light guide used was the same.

Sometimes heat is a good thing and can accelerate the curing process.  But some times with dark plastics heat can be a problem which makes selection of your curing technology critical.

What do you think?