The eye does a good job at dealing with the infrared. Not everyone's eye is the same, but someone that can see more infrared has been seeing it all of his life and it is integrated into how he perceive color.
The real problem is that the color is itself not a good indicator of temperature. Look at the frosted surface of an incandescent light bulb. It's color depends primarily of the blackbody radiation of the filament at lets say 3500K, but the glass envelope may only be about 400-500K. Sure, the glass envelope emits at a blackbody temp of 400-500K, but the color is pretty much that of the filament slightly reddened as it passes through the frosted glass (the frosting causes greater loss of blue). The alumina ceramic is a partly transparent envelope with a hot coil inside. Admittedly, the ceramic is more highly coupled to the heater coil and will be hotter, but the color is neither that of the hot heater coil (it is red filtered by the alumina) or of the color of the black body of its own surface. It is a mix, best characterized by measuring its spectrum. The Lugano hotCat had a different mix of heater coil light, ceramic color filtering, and blackbody radiation. For one thing the heater coil was different, thicker, and it was closer to the surface of the roots of the ribbed ceramic convection tube. Because the ceramic was thinner, more of the blue end of the heater coil spectrum would have made it through to the surace. The result is that the color in the VISIBLE range would have been more like that of the heater coil, because it had to pass through less ceramic [than the current dogbone]. There is discussion in the MFMP that it may be desirable to use a larger core to get the heater wire closer to the surface (roots) of the convection tube. Bob On Mon, Dec 22, 2014 at 2:46 PM, Jed Rothwell <[email protected]> wrote: > Bob Higgins <[email protected]> wrote: > > >> These effects conspire to make a simply taken picture taken nearly >> worthless in determination of temperature for this style of device. >> > > How about the color as perceived by the human eye? Is that of any value in > determination of temperature in this case? > > The eye is a remarkable instrument. > > - Jed > >
