I'll tell it again. We had power go out at NIST one Friday during the summer. No Air conditioning, and we were told to go home. Hot humid air quickly condensed on cool alkali halide crystal optics of laser setups in many labs, and next Monday all the optics holders were empty, and their bases were surrounded by little crystals. Many tens of thouands of dollars were lost, not to mention up to 3 months replacement time on some of them. One administrator looked at how low our electric bill was for that weekend and suggested that power be turned off every weekend.