>> You are of course correct about the thermos technically being a >> technically superior solution.It also has limitations which may or may >> not outweigh the gains compared to other alternatives. .... > I have to agree with Russell here. A thermos is good for only so long. > Eventually the inside of the thermos will reach the same temperature as > the outside atmosphere. The only way it could be better than a plastic > lunchbox is if it could be filled with dry gas - but then the lunchbox > trick can have the same dry gas fill. I wasn't meaning to disagree with Vitaliy - just note that I'd understood his point and that what I'd mentioned was similar in some aspects and different in others - both are complementary. Alan's various other suggestions were interesting as they unsurprisingly reflect some of the things I've thought about to keep sealed torches condensation free. If you take a waterproof light, heat it in the sun until it is nice and toasty hot and then cool it rapidly - bucket of water, stream, tropical shower etc - under some conditions you push the RH in the light over 100% and you get short term internal misting. This makes it hard to assess ongoing waterproofness and no doubt leads customers to wonder as well. I've considered dry gas purges and dessicants. More extreme solutions such as active dehumidification or internal heating would not be applicable in this context. One thing I've considered is a pressure relief passage filled with a suitable "grease" which allows pressure equalisation without breaking the seal. Potential for pumping problems over time. Bellow./diaphragm not too easy in a small device. We nominally rate the altitude range "Dead Sea to Base camp" more for fun than because those are real limits - they'd work OK on the top of K2. The Mini is pressure tested to 0.5 atmosphere during manufacture - so every one is known good to 14 feet deep. It's not intended as a diving light of course - the aim is to be able to service any amount of rain, river crossings, water trough, puddles and the like. Impact resistance - well OT now- is phenomenal. We say exceeds Mil Std 810 part xxx but in fact it's vastly superior. eg in actual tests the Mini typically survives 100 drops onto concrete from 1.5 metre+ random axis, 10 drops from 3 metres onto concrete and 3+ drops from 5 metres onto concrete. The 3 and 5 metre tests are "by eye" but could be formalised. 5 metres involves throwing the light to appropriate height and having it impact sickeningly and bounce away into the weeds. Great fun. I'll put up a video some time. After all that the light is still running but the outer is getting pretty scuffed by then and we've found a few points that degrade faster than others that will get addressed in due course, but overall its phenomenally impact resistant compared to almost any alternative. Unlike most, it can claim to be "soldier proof". Russell --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .