The light we put over the top is nowhere near even a fully shaded, black water habitat so all these fears are vastly overstated. I would suggest as far as they are verging on completely false let alone fearmongering.
If we put 6WPG over the tank we will still only just be matching a blackwater habitat that is under a full forest canopy!!!
As for the PAR, brightness, Lux etc. What we see as bright is not actual light. Just as wee see something bright and a certain colour, a bee sees it as a different colour and a dog etc.....Do we know what a fish ses as bright? Do we know what colours a fish sees?
There are many articles about the myths and the realities of animals seeing black and white or colour but is very hard to find anything that would detail what an animal sees as bright or how much light they actually see. light is different from colour so it may be that fish see more or less light than we do. Not in reality because they are seeing the same light however they may have more sensitivity to the light.
For example some people still believe that dogs see in black and white? They don't. They see colour just as we do however they are colour blind. So to a dog greens and reds can be the same etc.
http
/wiki.answers.com/Q/Do_dogs_see_in_color_or_black_and_white
http
/www.pattyvisioncenters.com/index.php/myth_busters/myth/animals_only_see_black_and_white
Where the myth may hold true a little (but not much) is the 'photo shock' suggestions however I would suggest it is far from damaging at worst a 5 second annoyance just as it is for a human to open the curtains and squint as our eyes adjust!!!
Be careful with the myths and the 'recommendations' Some are good to use as a starting base however most are way off the mark and are nothing more than someone 'deciding' X is a good idea or Y is not. We all have to sift through these things.
As for my observations when my lights come on automatically ( no human near to affect their behavioural response) the fish actually move closer to the surface. Closer to the light and therefore receiving more light. Why is this? I would suggest that when they go from dark to light conditions their sight can now see different colours and they go to the surface to see if there is any food there
I should add that my tank does have light 24 hours. It has the photoperiod of 9 hours but there are moonlights on for the rest of the time so there is always some light. Why do I do this? I have not had a single fish get caught in a filter intake when doing this. Before I did this it would have casualties when I came down in the morning. Take what you will from this anecdotal evidence as it is purely observation and correlated so there could be other reasons
Andy
