The average city sports a series of parks. These are open
spaces with various facilities for recreation and leisure
intended to somewhat offset the general misery of living
among altogether too many people. Often there are open
grassy areas that residents can picnic or sunbathe, sports
facilities
such as tennis & basketball courts, a children's
play area with swings/slides etc. and areas for dogs to run
around in.
These work perfectly well in summer where the sun does
it's thing. In winter however, the parks lose a large part of
their appeal. The grass becomes a mess of muddy patches
as the grass can't grow fast enough to offset wear, plants
lose their leaves covering the surfaces in damp rotting
leaves and the whole area becomes as dark, cold and
depressing as everywhere else.
So, let's replace the sun. LED lighting with carefully chosen
spectra can do a fairly convincing impression of the sun as
far as humans and plants are concerned. We need some
UV, plenty of blue through to orange but we can make
savings on the IR. So how feasible is this?
Taking as a model, Rittenhouse Park in the center of the
city I happen to be in is 3720 m^2, which at ~400W/m^2
would need in the region of 1500kW, and would consume in
the region of $120/hr in electricity. This is a lot, but not
totally unfeasible. Things get better quite quickly when we
think about it.
Firstly, we can probably pull off an LED impression of the
sun at half the power since we won't be doing any far UV or
anything more than a token amount of red. So, 750kW.
$60/hr.
Next, there is already daylight, we're just boosting and
extending it. Depending on your latitude, winter sun is
~1/2 the summer levels so we're down again to
500kW/$40/hr.
Next, our eyes trick us. Interior lighting at 20W/m^2
appears pretty bright because our irises open, despite
being 20-fold lower than daylight. So, by carefully
illuminating the least trafficked 1/2 of the park at 1/2
power, it's likely people wouldn't notice. Now we're at
375kW/ $30/hr.
$300/day for a small but busy city park is eminently
doable, and the health benefits in terms of vitamin D
synthesis and seasonally affected disorder treatment would
likely work nicely. The light source itself should be a point
source, either on a tower or cable-suspended from existing
buildings. Extra savings could be achieved by using a
dedicated combined heat/power generation. Excess
heat/power could heat the park slightly and power/heat
could be sold to nearby buildings or used as emergency
backup.