Kevangogh wrote:If I measure with a digital thermometer inserted into the water and scan with this thing on the surface, the difference shows less than half a degree. It's accurate enough, and certainly more convenient.
Anyone know if the IR type measures the surface temp of clear water or does it read further down?
Infrared radiation (IR) doesn't penetrate water too well. This is why water looks blue, because red light gets absorbed by water which then passes a larger proportion of blue light to our eyes. IR is just past red in the electromagnetic spectrum, so it is effectively even "redder" than what our eyes can see.
This effect is exploited by certain measurement devices in the manufacturing industry. You can measure the thickness of a water-based coating by seeing how much IR it absorbs.
EDIT: To answer the question, no, it pretty much just measures the surface. Sorry for getting off on a work-related lecture.