You kind of have to admire the sheer determination of the people in the Waffenamt, the Germans were actually making plans to try to negate the total allied air superiority by having the panzers attack at night using these infrared sights. The device was designed so you could aim the main gun using the infrared sight, by a complicated system of range estimating bars that went up and down with the gun and searchlight. So the commander could see the range by aiming the searchlight.
Here's a Panther with one of these gadgets attached to the commander's cupolla (sp?).

I was thinking of making one of these for my HL King Tiger but i've already got plenty to do on this, with the other mods i already plan to do. Bracing the hull, bushing the wheels (because most of them turn way too hard), changing the gearbox and redoing the paint to 1944 dunkelgelb base scheme. Still it would be quite a challenge-i can imagine maybe adding in a tiny red LED to the model of the sight.
Someone apparently made actually made a scale version of this infrared searchlight/sight for 1/35 scale tanks at one time, but the page from the site that sold them is gone. Here's the image of it

and the real thing again, rear view.

If someone has already made or wants to scratch build one of these, i'd sure like to see the pictures.