On Mon, May 27, 2013 at 7:04 PM, Joshua Cude <[email protected]> wrote:
> On Mon, May 27, 2013 at 5:22 PM, Harry Veeder <[email protected]>wrote: > >> >> >> On Mon, May 27, 2013 at 5:44 PM, Joshua Cude <[email protected]>wrote: >> >>> >>> But we have no idea what the emissivity of the paint used in the >>> December test was, nor whether it was wavelength dependent. There may be a >>> paint for which an assumption of emissivity of 1 greatly overestimates the >>> power. A few measurements could have excluded this possibility. >>> >>> >> >> >> This book >> >> _Absorption and Scattering of Light by Small Particles_ >> >> says for a body to have an emissivity > 1 it can't be much bigger than >> the wavelength it radiates. >> > > > > I'm not suggesting emissivity greater than 1. I'm suggesting we don't know > how the correction for a limited wavelength range goes for low emissivity > (this could be answered with a bit of effort, or by an expert in the area), > and more importantly, we don't know if the surface has a wavelength > dependent emissivity, in which case, an assumption of unity could err on > either side of the true value of the power depending on the particular > dependence. > If they take emissivity = 1 then they are assuming the worst value for emissivity at all wavelengths. How will a lower emissivity in any range lead to an over estimation of power? Harry
