There is an old science fiction concept of 'slow glass', where light travels very very slowly, with 1/2 day glass used for windows that allow light to dally for

There is an old science fiction concept of 'slow glass', where light travels very very slowly, with 1/2 day glass used for windows that allow light to dally for 1/2 day before it exits - also good for street lights. Extending it to week/glass, year glass and so on, with the glass becoming a defacto streaming video display to watch burglars/traffic etc. Interesting concept, smashing a pane of year glass - would it release all that energy as an e=mc2 blast?? https://sf-encyclopedia.com/entry/slow_glass https://sf-encyclopedia.com/entry/slow_glass