Yes, of course. The question I pose is: Does the outer color of the Reflectix really matter at night? I don't think it does. But some people act as if the outer color is the most important factor!
You do not understand radiative heat transfer. First of all, we aren't talking about visible light. Almost everything around the telescope radiates at a temperature of about 300K which peaks at a wavelength of 9-10 microns. To understand this stuff better, first go stand in front of a fire in a fireplace as you read this. The amount of power transmitted from a surface is determined by something called the emissivity, which describes how well the surface compares to a perfect black body. The color of the surface relates directly to the emissivity of the surface. Under stable conditions, the emissivity of a surface equals its absorptivity, so it emits as much as it absorbs. A shiny, aluminum coating (like on the surface of a mirror) or a very clean, white surface has a very low emissivity. As you stand in front of the fire, you'll notice that on the side of your body facing the fire, your skin is getting quite warm. That's due to the fact that your skin is absorbing heat in the form of radiation from the fire. There might be a bit of conduction as well but that's minuscule compared to what you are getting from the radiation generated by the hot embers. But don't go away thinking that this effect is only significant while standing in front of a hot fire. Radiative heat loss between your body and the walls of your house play a significant role in your comfort level at a given room temperature between winter and summer. This is why a thermostat setting of 70F in the summer might seem a bit warm; whereas, you might be too cold at the same setting during the winter.
When your scope is under the sky on a still night, roughly half of the heat exchange comes from radiative transfer. I recently calculated the effect for a piece of glass exposed to the full night sky and found that the front surface will stabilize at between 7 and 11 degrees below the ambient air temperature (depending on the temperature and humidity.) That's why you get dew on the optics and also it's why the inside of a sealed telescope (like a SCT or refractor) can get wet or frosted (on a cold night.) It's also a big reason why you get thermals inside the tube. I've personally seen split imaging from a thermally stabilize C14 XLT with a black tube on cold, humid night due to radiative cooling of the tube, which caused a stable thermal temperature gradient inside the tube.
Reflectix does two things: 1) It reduces radiative heat loss to the sky, and 2) It reduces convective heat loss from the tube to the surrounding air. Both of these effects greatly slow thermal stabilization of the system. The problem is that the front optical surface will still be exposed to the sky so it's still possible to get natural convective air turbulence within the tube. It's better (meaning less turbulent) than the currents produced by not having the Reflectix, but in my experience, it simply prolongs the time to get to a well stabilized system--and that's not desirable. The best solution is to prevent radiative cooling on the tube while using forced convection to more rapidly bring the OTA to thermal stability. In my experience under a wide range of conditions using a SCT, I've found that Tempest fans are an excellent solution. They provide only a small amount of air exchange with the outside air and the circulation is very small, but it is perfect for preventing temperature gradients, baffle currents, and for more quickly bringing the OTA into equilibrium with the outside air. So, in my view, Reflectix on its own is only half of the solution. To get the best results, you need to do both: 1) Wrap the tube in Reflectix, and 2) Use fans to provide a small amount of outside air circulation within the tube.
It's clear that you are not alone in struggling to understand this stuff. In this thread alone, it's apparent that a lot of folks don't understand the differences between conduction, convection, and radiation and the roles they play with respect to image quality and dew prevention. The article that I'm working on will explain this stuff in a lot more detail. Hopefully, going through a bit of the underlying physics will help to dispel myths and raise the collective understanding a bit.
Edited by jhayes_tucson, 27 November 2018 - 01:33 PM.