Thanks for the replies. I'm planning a longer session today. To a dull 75 year old the thought of getting "hyper" is attractive particulary if I can do it while finishing off m tax self assessment....
I've just acquired a 10k lumen box which advises 1 hour per day at 20cm or 2 hours at 50cm. Following a suggestion in the forum I positioned the lamp just above my laptop. This was great - so much...