Earlier in the session, Alex Salmond and Sir John Elvidge, Scotland's top civil servant, gave evidence into civil service co-operation and communication.
And, venting his frustration, Mr Henry, the former Labour education minister, swore in the presence of Scotland's top civil servant, Sir John Elvidge, when he appeared before the committee.
The extent of the problem, at least at optical frequencies, has recently been catalogued by Pierantonio Cinzano and Fabio Falchi at the University of Padua, Italy, and Christopher Elvidge at the National Geophysical Data Centre in Boulder, Colorado.