I also found the Telegraph's explanation lacking. Their explanation they give makes me think that the interior of the glass bulb has some coating or special com

I also found the Telegraph's explanation lacking. Their explanation they give makes me think that the interior of the glass bulb has some coating or special composition. This impression is quite distinct from the reality of the filament between plates with alternating layers of SiO2, TiO2, Al2O3 or Ta2O5. The Telegraph could have at least said that the advance involved sandwiching the filament between layers of transparent material that transmit light by reflect IR. Not to mention conflating crystal structure and glass. (Glasses can be distinguished from crystals by a lack of repeating long range structure).