Quantum Dot LEDs: the future of lighting?

[JoeStrout]

We're going to be working on lighting for version 0.17 (though right now we're focused on water).  This news story today seems quite relevant:

Quantum Dots Enable Next Generation of LED Lighting Systems

Pretty neat stuff!  Perhaps these are the direct ancestors of the artificial sky in future space colonies?

[JoeStrout]

We're making progress on the lighting now, so we've returned to this issue.  Re-reading the article above, I'm convinced that this really is the future of lighting (until something even better comes along!).

These new quantum-dot LEDs have power densities about 300 times those of current devices.  And current LED lighting is already really bright — I have a strip of surface-mount LEDs on my workbench right now, and they're almost painful to look at from half a meter away.  But of course we're talking about making a "sky," i.e., lining a roof that may be more like 100 m or more away.  To produce outdoorsy levels of illumination on the ground, we're going to need all the power density (and efficiency, to avoid waste heat) we can get.  It looks to me like these LEDs can deliver.

For High Frontier, the question we're facing at the moment is: how much will panels of this stuff cost?  And I have no good way to estimate that.  But the fabrication process is very encouraging:

Quote:Perhaps the most appealing aspect of the research is that the new LEDs were entirely fabricated through solution-based processing carried out at room temperature and pressure.

That almost certainly translates to "cheap" except in cases where the materials themselves are expensive — but these things are made of conductive polymers and silicon.  Nothing particularly pricey (or hazardous) there as far as I can see.

So we're going to pull a reasonably low cost per square meter out of the air, and tweak it for gameplay balance.  But if anybody has any thoughts on the matter, please do speak up!

[JoeStrout]

Oh yeah, and in case anyone's curious, here is our reasoning for how much power is required for artificial lighting.

Pure sunlight on Earth is 1.4 kW/m^2, but clouds reduce that by 90% or so, while still remaining quite bright outside. It seems silly for space colonists to need sunscreen and hats to protect themselves from the artificial light, so let's assume a base target of 15% full sunlight.

We can assume that artificial lights will be quite efficient, but not perfect. So, end-to-end, we'll consume 20% of full sunlight power, or 280 W/m^2.

[Sailor Barsoom]

(07-13-2015, 09:29 AM)JoeStrout Wrote: Oh yeah, and in case anyone's curious, here is our reasoning for how much power is required for artificial lighting.

Pure sunlight on Earth is 1.4 kW/m^2, but clouds reduce that by 90% or so, while still remaining quite bright outside.  It seems silly for space colonists to need sunscreen and hats to protect themselves from the artificial light, so let's assume a base target of 15% full sunlight.

We can assume that artificial lights will be quite efficient, but not perfect.  So, end-to-end, we'll consume 20% of full sunlight power, or 280 W/m^2.

They won't need sunscreen or hats because the UV will be much less than on Earth.  Redheads can go skinnydipping at noon!

Is your idea to basically make the ceiling (in habitats that have one, like a torus) into a giant TV screen?  That would be pretty cool.

[JoeStrout]

You're absolutely right about the UV.  Maybe I should say, I don't think it should be so bright you have to wear shades to go outside (though you may still wear them for style, of course!).

And yeah, the basic idea is to have the ceiling (or a central tube, in the case of something like a sphere) covered with LED (or some future equivalent) light panels.  I wouldn't call it a giant TV screen because it's not really meant for displaying images... though I suppose, given light panels and how cheap electronics are, there'd be no reason you couldn't turn them on and off to create some animated patterns.  (But I assume RGB capability would be quite a lot more expensive than plain white.)

[JoeStrout]

Stephen Covey pointed out a blog post he did on this subject in 2009: Lighting our Space Habitats.

He argues eloquently that artificial light makes far more sense than natural light for a space habitat, and backs it up with numbers.  Of course his numbers are from 2009; lighting has gotten even better in the six years since then, and will almost certainly get better still in the coming decades.

So I have to agree with his conclusion, though of course in the game, we'll let you try it both ways.

Speaking of which, here's a sneak peak of what we were working on today...

But seriously, go check out Stephen's blog, which makes a refreshing amount of sense!

[FlyingSinger]

This should be right up my ally as an optical engineer, but I don't know much about QD's right now. I do know that it can be very challenging to scale technologies that work well in the lab to product-level size, lifetime, efficiency, cost, etc., though it's true that QD LEDs sound promising as far as non-exotic materials and fab techniques. OLEDs (organic LED's) have been in development for years and even used in some small displays in products. Samsung has shown OLED TV's at lighting shows, but I don't think they reached production. At one point (maybe 6 years ago?) many articles in the illumination world suggested that OLEDs would eventually replace regular LEDs (and their associated reflectors, lenses, etc.) and other light sources in many or most applications, at least for displays if not for lighting. But OLEDs didn't scale well to larger sizes and higher efficiencies and lifetimes. And regular LEDs just get better and better and cheaper as they make zillions of them.

Artificial lighting is clearly the way to go, as mentioned in that blog post and other sources. In Stan Robinson's new book "Aurora" the space habitat is actually a generation starship that has been underway 160 years. Solar power not an option for most of that time (nuclear fusion is -- he sets this book in the 2700's). He doesn't describe their technology, but the the "sky" of each of the micro-habitats in the Aurora sounds like a QD-like device, huge panels of them with greatly tunable light output and spectrum, so it can be set to simulate different seasons and latitudes and altitudes for the flora and fauna of each module (each such "biota" is about 4 km long and there are 12 of them in a ring, IIRC). The rings are spun for 0.83g which is the G of the Earth-like planet they intend to colonize (moon of a gas giant orbiting Tai Ceti, actually), so when the 6th generation people who plan to live there arrive, they will have lived their whole lives in this G. But watch out for Coriolis force changes when you start to decelerate the ship... could plants be sensitive to such changes? This is the level of detail that KSR can reach.

It will be interesting to see if I (or someone) can build a model of the Aurora in High Frontier sometime. Here's a picture (notice it has two independent rings, though you can move between them via the spine):
Kim Stanley Robinson's Aurora generation starship.

If you are interested in space habitats, Aurora is one of the most vivid and detailed depictions I have ever read. So many interacting factors. And a good story. I just transferred a discussion of the book from my journal to my blog here. 

-Bruce

[JoeStrout]

OK, there's another one for my reading list then!  I love hard SF.  A good book should make you think — and not about dreamy vampires, but about real possible futures for humanity.


I don't see why you couldn't build something very much like that Aurora design in High Frontier.  I'll paste the image in here in case anybody's bashful about following the link:



So, two torus sections, joined with what in HF would have to be some box sections.  (Adding non-rotating cylinder sections, for just this sort of design, is on our to-do list but hasn't made it to the top yet.)

I wonder whether this design would be rotationally stable, though.  Even with the two torii counter-rotating, I worry that it would end up tumbling end-over-end.  It'd be more stable if you shortened (or removed entirely) the distance between the torii, so the spinning mass is as close to the middle as possible.

Anyway, as for the QD lighting, you're right, it may never turn out to scale up as well as LEDs.  But this just shows what a happy position we're in — we have so many promising technologies, our difficulty is figuring out which one is going to come out on top!

[FlyingSinger]

Joe wrote:
I wonder whether this design would be rotationally stable, though. Even with the two torii counter-rotating, I worry that it would end up tumbling end-over-end. It'd be more stable if you shortened (or removed entirely) the distance between the torii, so the spinning mass is as close to the middle as possible.

I'm sure you've developed good instincts about such things, and a tool that can probably test it out. Keep in mind this book cover image is just an artist's conception based on KSR's descriptions and perhaps sketches. Stan credits a lot of technical helpers, so there may have been some modeling done of some aspects. He probably needed dimensions and other details to define some of the action in the book. But they may all be back of the envelope approximations.

[Sailor Barsoom]

If you have habitats like this, why do you even need to colonize an alien planet? I started a discussion on Amazon called "Planets: Who Need 'Em?" Some people made some good points, and some people... Ay ay ay!
https://www.amazon.com/forum/science%20fiction/ref=cm_cd_pg_pg1?_encoding=UTF8&cdForum=FxWK0QNW07Z4M7&cdPage=1&cdThread=TxKUFJK7E91Y44