I dunno, have you ever been around glass blowing? It gets pretty bright
I think this is a question of surface area.
Based on this calculator
http://www.spectralcalc.com/blackbody_calculator/blackbody.php , and my limited
understanding of radiance, a 1400C (~1700K) black body radiator will emit
around 4700W/m^2 from 400nm to 800nm, approximately the visible range. In a
glass blowing furnace filled with hot material transparent in to these colors
of light, I can imagine the surface area of the emitter could be quite high.
So you open an imaginary glass blowing furnace with a surface area of 1m^2 you
see a 4700 W lightbulb. Very bright!
However the same furnace is radiating much more light in the invisible
infra-red wavelengths. Again based on the calculator in the link, the 1700K
material is emitting 742 000 W/m^2 in-between 800nm and 12micons in the
infra-red.
The fraction of light in the visible is given by: VISIBLE/VISIBLE + INFRA-RED
= 4700/4700+742000 = 0.6% of the light
So for the Rossi experiment. If the total power radiated is 2400W then the
intensity in the visible will be 2400W*0.6% = 14W radiated in all directions.
A 20cm by 2cm cylinder emitting 14W of visible light is not very bright at all.
All these calculations are approximate and I literally just looked up band
radiance from a blackbody emitter for the first time 20 minutes ago so I could
be wrong. But as a photonic materials chemist it makes sense to me.
Of course, there are Nobel laureates loitering in these threads, so maybe they
can critique the above.
I also think the transparency of glass may make it appear brighter, because
light emitted within the bulk of the material may not be reabsorbed.
For instance, lava is a similar temperature to glass but is not nearly as
bright as a glass blowing furnace, because only light emitted at the surface of
the lava can escape to hit your eye.
