210cm vacuum tube assimilate the advanced 12 layers of spattering deposition of trivalent element technology to make the tube has high performance of absorptance and low reflection ratio. It also can stand up to high temperatures and perform a strong heating ability. And improve the deposition layer's structure through add rare metal to enhance the effect photosensitive reaction, the absorbing rate of vacuum tube up to 0.96. Absorbing rate can be raise over 16% than 180cm vacuum tube. So it can be heat if cloudy�