Great glasses I have been using for decades!
I have just retired after a five decade career of teaching Astronomy, Space Science, and related topics in planetariums and science centers. For almost three of those decades, I have been using these diffraction grating glasses to teach about light, spectroscopy, emissions from spectrum tubes, distance to stars, red and blue shift, the Doppler Effect, etc. My latest purchase is for my friends to watch fireworks through on the fourth of July at our annual party. We have been using them at our party for the last eight years!