4 ms·

If your plan is "light pipes, but fall back to LEDs" that means you have to build two complete systems. You get double the installation costs, incur the combin

If your plan is "light pipes, but fall back to LEDs" that means you have to build two complete systems. You get double the installation costs, incur the combined complexity of both systems (plus overhead), and box yourself into the limitations of both systems.

kragen 7y ago
That might be true, but I'm not sure it is. It seems to me that you escape the limitations of both systems. Also, I think lightpipe daylighting generally costs orders of magnitude less than sunlight-comparable LED illumination, although I don't have firm numbers on lightpipe costs; so I don't think the installation costs double, just increase slightly. If we're talking about a greenhouse, where a leaky roof is a minor annoyance comparable to a leaky faucet, rather than a life-destroying disaster, lightpipe costs should go down quite a bit compared to their use in office and residential daylighting. The big question for me is, if you're going to build a hothouse, why would you build it with an opaque roof? That just seems perverse, like writing an HTTP server in bash or assembly language or something: http://canonical.org/~kragen/sw/dev3/server.s http://canonical.org/~kragen/sw/dev3/server.s
- rini17 7y ago
  Efficient light pipes require solar concentration and thus tracking. That will drive costs up. Current residential/office light pipes are using only small fraction of sunlight, so they aren't relevant to this problem at all. Also you haven't said anything about cooling, which the translucent roof inevitably requires in summer.
  - kragen 7y ago
    These are good points. Lightpipes can use non-imaging optics in many cases and thus avoid the need for tracking, but maybe not in this case, and I hadn't thought about that. Cooling, though, is an issue whether your light comes from LEDs or the sun—either way it comes with a lot of extra heat. With the LEDs I'm familiar with, this is a worse problem than with sunlight, but in another thread https://news.ycombinator.com/item?id=20908476 https://news.ycombinator.com/item?id=20908476 I see a report that there are now illumination LEDs that reach an astounding 40–50% efficiency level. If that's true, it would make the LED cooling problem a little smaller than the sunlight cooling problem, instead of much bigger; and of course spectral matching helps.

kragen 7y ago

That might be true, but I'm not sure it is. It seems to me that you escape the limitations of both systems. Also, I think lightpipe daylighting generally costs orders of magnitude less than sunlight-comparable LED illumination, although I don't have firm numbers on lightpipe costs; so I don't think the installation costs double, just increase slightly. If we're talking about a greenhouse, where a leaky roof is a minor annoyance comparable to a leaky faucet, rather than a life-destroying disaster, lightpipe costs should go down quite a bit compared to their use in office and residential daylighting. The big question for me is, if you're going to build a hothouse, why would you build it with an opaque roof? That just seems perverse, like writing an HTTP server in bash or assembly language or something: http://canonical.org/~kragen/sw/dev3/server.s http://canonical.org/~kragen/sw/dev3/server.s

rini17 7y ago
Efficient light pipes require solar concentration and thus tracking. That will drive costs up. Current residential/office light pipes are using only small fraction of sunlight, so they aren't relevant to this problem at all. Also you haven't said anything about cooling, which the translucent roof inevitably requires in summer.
- kragen 7y ago
  These are good points. Lightpipes can use non-imaging optics in many cases and thus avoid the need for tracking, but maybe not in this case, and I hadn't thought about that. Cooling, though, is an issue whether your light comes from LEDs or the sun—either way it comes with a lot of extra heat. With the LEDs I'm familiar with, this is a worse problem than with sunlight, but in another thread https://news.ycombinator.com/item?id=20908476 https://news.ycombinator.com/item?id=20908476 I see a report that there are now illumination LEDs that reach an astounding 40–50% efficiency level. If that's true, it would make the LED cooling problem a little smaller than the sunlight cooling problem, instead of much bigger; and of course spectral matching helps.