Hopefully I'm not opening a whole can of worms here
Have you ever considered making a UV meter to help pt pd workers controlling density outside?
I think a lot of it comes out of simple frustration with how most of the "easy options" for getting calibration standards come across as a bit wishy-washy as to their traceability, but more importantly that you can't actually get off-the-shelf calibration references anymore for a lot of density measurements.I understand your desired to adhere to existing calibration standards, if only to create a common baseline with existing/legacy products out there. On the other hand, I doubt many people who buy your devices will actually use them side-by-side, let alone interchangeably with such equipment. So I wonder how hard you should be on yourself/your developments in trying to adhere to these standards - although I'll happily admit that from a marketing perspective, it looks good.
As far as UV wavelength, my first driving factor was attempting to get as close as possible to something else people might familiar with and/or have used before. That would be the X-Rite 361T. Now there's nothing official out there actually stating what "X-Rite UV" actually means. But I have found a few clues. First, I tried shining light into the sensor head while sweeping its wavelength with a monochromator. I found that readings peaked in the ballpark of 390nm. Second, I found some X-Rite marketing sheets which mentioned the key-word "diazo". In ISO 5-3:2009, that suggests "Type 1 Printing Density", which is around 400nm.The reason I'm bringing it up is the wavelength issue. Perhaps even more so than the VIS domain, wavelength makes a massive difference in terms of UV transmission density of materials. Combined with the proliferation of LED technology, which is fairly narrow-bandwidth by nature, this can create rather massive differences between measurements done at e.g. 365nm vs. 395nm. In a bit of a niche application (although seemingly gaining popularity), it turns out that for DAS-sensitized carbon transfer, a combination of exposures at different wavelengths is beneficial in optimizing shadow and highlight behavior in the same print. See e.g. Calvin Grier's work in this domain, and my own experiments and present printing methods are in line with this.
In practice, it wouldn't be too hard to make a version with a 365nm UV LED. The problem is that the 365nm UV LEDs aren't as bright, and I'd basically need to invent my own calibration standard (likely based off that spectral data) to handle it. And it would be an either/or type of decision, since having both in the same unit would be too major of a change.Long story short, I think there's a use case (but perhaps a relatively small market potential) for differentiation in wavelength. I wonder to what extent this present development of yours could still be augmented to accommodate this kind of functionality.
The farther into the UV range you get, the wonkier the transmission spectrum of film becomes.
So I decided to include a temperature sensor next to the light sensor, and put together a calibration-and-correction process.
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