On 14/08/2013 17:59, Chris Hogg wrote:

A calculation: sunlight's composition at ground level, per square
meter, with the sun at the zenith, is about 527 watts of infrared
radiation, 445 watts of visible light, and 32 watts of ultraviolet
radiation (from http://en.wikipedia.org/wiki/Sunlight). Call it 450
w/m^2 of visible light, or 0.045 w/cm^2, or 22.2 cm^2/w.

If a bottle delivers say 50 watts of light, then each bottle will have
to have a cross-sectional area of 50/0.045 = 1110 cm^2, or a diameter
of about 37.6 cm. So they'd have to be even bigger than Jeff
suggested, which makes me think the estimate of 40-60 watts is
somewhat exaggerated.

Yes, I was mistakenly basing my calculation on the approx 1000w/m^2 of
total solar energy delivered perpendicularly. I hadn't taken into
account that only around half is visible. I had also assumed that when
the term "water bottle" was used in the article, it was referring to
those large bottles found on water coolers.

--

Jeff