devicephotodiode
In the literature, I often see the notion of square law devices. Why are these devices important, to the extent that they have their own characterization as square law device?
In what context does this square law property become relevant, except the fact that it characterizes the relationship between an input and an output parameter for that device.
It's because they use hi-res colour displays. There is so much light lost through colour displays that they need a backlight to provide good contrast. You lose 50% through the polarizers, then about two-thirds through the RGB filters, so less than a third of the light makes it through.
If you're thinking about ISO-9000 that's about the quality of your organization and its processes, not your products. You can have ISO-9000 certification and still produce the worst crap.
There are certification organizations, like Underwriters Laboratories in the US and TüV (Technischer Überwachungsverein) in Germany. Many components won't have certification, though. You'll find it mostly in safety sensitive components, like where isolation from mains is important.
Other organizations, like IEC (International Electrotechnical Committee) write specifications, but don't certify.
A good manufacturer should hand you its own testing procedures for its components upon request, as well as test reports. Those are sometimes included in datasheets.
Some will refer to certification organization standards, like shown in this snapshot of a random Littelfuse datasheet:
Note that the Underwiters Laboratories (the top logo) and PSE (Product Safety Engineering) logos refer to their respective certification, while the CE logo doesn't imply this. (The CE logo means that you claim to comply with CE standards).
Best Answer
It's a particular classification of nonlinear behavior that has important applications.
In the same way as you can consider, say, a BJT as linear over a limited range, you can consider something like a diode as square law over a limited range. That simplification allows you to analyze functions such as RF detectors analytically.
See, for example, this Agilent paper "Square Law and Linear Detection".