BLR...
Try to think of "light" from a different perspective/level...
Light (that we can see, as well as spectrums we cant see), just like radio waves, heat, microwaves etc etc...are all forms of radiation...that radiation being energy that is either emitted from, or reflected off of an object (in this case your little piggy going to BLR's 243 market)...
Either that, or expand your thinking to allow yourself to accept that all forms of radiation are different types/forms of "light"....& the thermal picks up/sees a particular "section" of that radiation/light.
Thats why if you search astronomy pictures, you'll see different nebulas/galaxies/stars etc a different colour from the next or last pic of them...you might even see a pic of a galaxy where one pic of it is huge as compared with the next--because the different forms of "radiation" (or "light" if you like t call it that), that the picture has been captured with, show up a different spectrum that cant be seen by the last picture form.
So there are pics of say a given nebula in our galaxy that have been taken with light that we can see, as well as the same pics taken with certain frequencies (wavelengths--what ever they are) say microwaves & radio waves that have different colours & show different aspects of the galaxy.
Kind of like how we cant see infrared spectrum without it being transposed into wavelengths on a screen that we can see...
I really dont know how well im explaining this...so im gonna go & have a scotch...
& i thank you for the excuse to do that BLR...
Hope ive shed some light on the subject for you...
...ah fark i crack myself up sometimes...!!
The man who knows everything, doesnt really know everything...he's just stopped learning...