I selected to try on this 20x-high is the 18" Beamswork DA FSPEC LED Aquarium Light Pent Freshwater 0.50W - https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
I got the optional timer module for it, but not sure if I'm going to like it or not. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Using our Apogee PAR meter, simply in the "electronic" mode, I measured this to be as low as 20 PAR at the floor of the tank, and closer to 200 at the top.
Incidentally, when discussing this today with a friend of mine from the Orchid world (yes, I'm probably going to put some really fun stuff in here), he was discussing light intensity with me in terms of Foot Candles....OK...so...how do we go from FC to PAR?
I did some digging around looking for a conversion, specifically asking how much PAR is in 1 foot candle of sunlight. That number actually turns out to be 0.02...more or less it would seem. Thus, a plant experiencing a range of 800 to 1400 Foot Candles of light in its natural environment, that might roughly translate to 16 to 28 PAR....and so long as all those numbers are correct, that means my two very special orchid selections for the floor of this vivarium are going to fare quite well with the "20" min that they'll be getting!