Enhanced Light Public Park

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.