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I would like to have a small orb, producing light of proportions of a standard household bulb today. No big deal, right. They have these already for sale on Amazon as night lights.

I would, however, like to create a floating version of this, anchored above shoulder height of its owner, providing a moving, ambient luminescence.

Some considerations:

  1. Power- This light should be able to last for months on end. I envisioned something powered by possibly a small RTG, as it would supply constant power for long periods of time.

  2. Staying Airborne- I would prefer for this light to be perfectly spherical, with no large protuberances. How could I make this lighter than air?

  3. Cost- I'm sure its no difficulty making one of these expensive, and I originally intended only the wealthiest class to be able to afford them readily.


I don't feel committed enough to this small facet to change the time period from that which I was originally imagining: No more than 400 years into the near-future. Assume, for example, that aside from cheap-spaceflight, we are still bound to our solar system by failing to achieve FTL travel.

How do I make a glowing, floating, and long-lived light source that can be used in every day situations?


I would like to keep this as realistic as possible. Not too much handwavium.

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I'm guessing this is a strictly sci-fi question, no magic. Am I correct in this assumption? – XandarTheZenon Jan 15 at 21:34
    
You say "standard household bulb," but the link you give is for a nightlight. Are you looking for nightlights, or something you could comfortably read under? – Cort Ammon Jan 15 at 21:37

You don't even need to go all super-futuristic for this. It's almost possible today. Get a balloon filled with helium, and put a small LED button-battery powered light source inside it. Secure it with some ultra-fine fishing line, attach the other end to your clothing, and you're basically done.

Now if you want it to look nicer and slightly more future-techy, you can replace the balloon with specially molded ultra-thin lightweight composite, maybe with a well-placed strut to keep the LED centralized (and possibly provide an external power switch and means of replacing the battery), and replace and the fishing line with carbon mono-filament. Anything else is just over-engineering.

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Yes! I think the most probable line of development is the improvement of LED brightness and efficiency coupled with improvement in battery power density (so batteries get lighter) and this will be very feasible. We can already make the electronics small enough if we want to make the thing autonomous. And hobbyists are already making super tiny motors that can be lifted by balloons (heck, the radio controlled shark balloon proves that the core ideas are feasible) – slebetman Jan 16 at 5:30

To make an object light enough to levitate without a large engine, rotors etc, arrange for the light to receive power remotely. Inside a building or around the perimeter of the yard are microwave emitters which provide the energy to power the lamp, and the associated systems that keep it flying.

If it is light enough, I would go for Electrostatic levitation https://en.wikipedia.org/wiki/Electrostatic_levitation or electrohydrodynamic (EHD) flight https://en.wikipedia.org/wiki/Ionocraft. This provides a relatively quiet and unobtrusive means of flight, few or no moving parts and in the case of the EHD device, it might be self illuminating under certain circumstances without an internal light bulb.

In order for the user to enjoy the lamp without being fried by the energy beam, a simple precaution might be for each emitter to produce a fairly low energy microwave beam, but the lamp receives enough power to light up and fly by intercepting two or more beams. With handshake technology to ensure the beams are pointed at the power target and not at the user, and enough intelligence built into the system to track the lamp and have the lamp track the user at all times, this seems fairly doable even with today's technology.

The lamp itself will probably resemble a traditional Japanese lantern with a "rice paper" cover to ensure the total weight is very low, and the LED and various computational devices and power targets concentrated on the bottom in order to ensure stability. The "rice paper" would actually be a fairly sophisticated composite which may double as the electrodes for the flight system or the power target, and the entire device would be between the size of a softball to a beach ball, depending on technical factors and perhaps "fashion" (higher status people could afford the very sophisticated systems of a small lantern, while other people would need larger, less sophisticated lamps. Very poor people might need foil lined hats to protect them from the side effects of being too close to cheap North Korean knock off lamps....

Or you could just use these: Paper lanterns

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Electrostatic levitation looks to only have been demonstrated in a vacuum chamber -- and the problem with EHD is that you're dealing with kilovolts ;) – Wingman4l7 Jan 15 at 20:12
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But it will be pretty spectacular when the method of emitting light turns out to be coronal discharge... – Thucydides Jan 15 at 20:14
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+1 for the Japanese lanterns! Now replace the rice paper with a single molecule thick, nano-assembled membrane and the candle with an extremely slow-burning alloy of phosphorous to provide heat and light. Anchor it with another nano-assembled product, a nearly invisible thread, and you have a high-tech to produce, low tech to operate solution. Perfect to use as a fashion accessory for the rich. – Henry Taylor Jan 15 at 20:19
    
@Wingman4l7: Electrostatic levitators work in normal atmosphere fine. Search youtube for "lifters" (ignore the anti-grav mumbo-jumbo from people who don't know physics, they're electrostatic levitators). The problem, as you've mention, is the kilovolts - it wouldn't get approval from any standards body, much less a CE or FCC rating, so you can't sell it to the general public. You wouldn't want to anyway since the first person electrocuted by it or the first house burned down will sue you. You were probably thinking of the reactionless EM drive. – slebetman Jan 16 at 5:27

Getting it to float is actually pretty interesting.
First, to get it to stay over the user you'd want it tethered. This means that the light doesn't need to carry it own power source.
To get it airborne the user would wear an algae bioreactor, which would create hydrogen. Some of the hydrogen would be used to fuel a small fuel cell, and the rest would be piped up the tether to the balloon, causing it to float.

The light source would be fairly easy, with an array of low energy LEDs powered through the tether and insulated to avoid sparking.

If there was a spark, a party balloon size explosion wouldn't do enough damage to cause harm, other than hurting your ears.

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If it has controlled flight (my quadcopter suggestion) the "tether" could be proximity based to a registered identifier (optical, whatever). But a physical tether would allow for alternative power sources. – Draco18s Jan 15 at 19:50
    
@Draco18s Yeah. I was mostly trying to figure out how to keep it spherical. The nuclear power idea would be interesting, but probably realitivly heavy, so powering a quad copter through the tether might make some sense even in that situation. – AndyD273 Jan 15 at 19:57
    
The nuclear approach is just the power:weight ratio is so very high, on the fuel end of things. The power plant might be too bulky, but in a sci-fi setting I've seen personal force fields powered by a quarter-sized sphere that was a nuclear battery. Of course it was used by high-tech con men on lower-tech marks, as it had a lifespan of only a few days. How small such things could get in 400 years isn't something a reader would be able to accurately guess, so it doesn't break the suspension of disbelief. – Draco18s Jan 15 at 20:04
    
the buoyancy of hydrogen, albeit being the biggest we have save vacuum, is still not much. – njzk2 Jan 15 at 20:14
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20L balloon gives you 24g, needing apparently a 0.35 m^2 shell, which, using the lightest fabric I can think of is ~5g, which leaves 19g for the led and power. can be done indeed! – njzk2 Jan 15 at 20:23

Staying Airborne

One method of staying aloft which is usually overlooked is using a vaccuum. Such a concept was originally proposed in the 17th century, but materials constraints limited its applicability. A 2006 patent application suggests a layered wall with a honeycomb structure sandwiched between, possibly using exotic materials like beryllium, boron carbide ceramic, or "diamond-like carbon". So, off the cuff, I would suggest some sort of nano-constructed, nested buckyball design for maximum strength.

The appeal of using a vacuum to stay aloft is that you don't have juggle with the classic problem of generating enough lift to overcome the weight of your power & fuel supply, while still carrying a useful payload. However, even if you assume a very good vacuum (and thus the full lift potential of the displaced air), you're only going to get about 1.28 g of lift per liter of displaced air (the density of air @ standard temperature & pressure). I hope you're using lightweight LEDs!

Power

With such a restrictive weight limit to keep it to a reasonable size, you'd ideally want to omit including the power source within the device. Beamed laser power would provide a possible solution, with the laser & power source concealed on the owner's person. NASA made a proof-of-concept of this, shining a laser on photovoltaic cells hanging from model airplane to power its electric motor while in flight. Another option might be resonant inductive coupling, but I am uncertain if the power requirement / efficiency / distance involved would make this feasible.

Depending on the output level of light you're looking for -- you said "ambient luminescence" -- you could cut the requirement for electrical power completely by using a bio-engineered light source. Perhaps a bacterial coating on the sphere, able to photosynthesize for energy storage, later combining the stored glucose with oxygen to synthesize ATP and generate a form of bio-luminescence.

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overlooked because there is no known material capable of withstanding that kind of pressure. And any puncture is instantly fatale. – njzk2 Jan 15 at 20:15
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also, vacuum gives you 1.292g/L, and hydrogen gives you 1.202g/L. That's a difference of ~7%, so the tradeoff is likely not worth it, giving how light it is to build a small hydrogen-proof (more or less) shell – njzk2 Jan 15 at 20:17
    
@njzk2: I don't think you're correct -- it's as much of an engineering / construction problems as it is a materials science one. Why would a puncture be fatal? A vacuum sphere would cause the materials to violently collapse, not explode. – Wingman4l7 Jan 15 at 20:18
    
fatal to the buoyancy. But using a gas balloon, there is no need to have any pressure difference between the outside and the inside, so in case of puncture, the gas would just leak away very slowly. – njzk2 Jan 15 at 20:25
    
@njzk2 In case of a vacuum nanostructure a puncture can hardly be instantly fatale. I mean it might pierce one of the billions of vacuum inclusions in the structure (likely not, but maybe), but it would only cause a slight decrease in lifting power. – mg30rg Feb 18 at 14:59

This started as a comment to Wingman4l7's excellent answer, but it got too big.

Reasonable size for such orb would be about 2 liters. So you have maximum 2.6g of lift. Assuming really lightweight walls and vacuum inside, it gives you 2g of useful lift.

With laser, mounted on owner's shoulder, you do not need photovoltaic cells and LEDs. All you need is to diffuse such light - just the way prop light sabers are doing it. Thus, sphere would be glowing - the beam delivering light to it would be hardly visible.

Alternatively, you could use luminophore and pump it with UV. And if your luminophore can both be pumped by radioactivity AND shield against it, you just need a small drop of radioactive substance in the sphere's centre to be good. I don't know of any such material, but it doesn't mean some composite ones won't be developed in near future. There are small key chain lights made using this approach, but there is hardly any shielding, so they have to stay small to keep radioactivity at safe levels. But we aren't that far from it.

For staying in place, it'll be more tricky. Tethering it by using regulated electromagnet, in a way levitating globe toys are doing it, would be doable, but would not affect position in any way. Lamp would stay behind it's user when in motion, and float above electromagnet when he stops. I see no real way around that.

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Just when I think I'm being clever, you really take it up a notch -- +1! Maybe tritium would do the trick? Isn't that how those key fobs work -- a small piece of tritium inside a phosphor-coated tube? – Wingman4l7 Jan 15 at 23:43
    
@Wingman4l7 yes, but they only make really, really small tubes - because there is no real shielding. Won't work in 2-liter scale. But almost, almost. – Mołot Jan 15 at 23:45

If you don't mind going nuclear...

A small nuclear powersource might be possible (or at least, feasible to your readers) which will last for a few years, even while powering a low-wattage light bulb and the flight system. This is the kind of powersource we've given to a number of our space probes, although those tend to be "small car" sized objects rather than "softball" sized. But with sufficient amounts of FUTURETECH! people won't give it too much thought.

Then, keep it aloft via quadcopter magic.

Alternative levitation might be achieved via electromagnetism, depending on the material composition of the surrounding environment (inside a spaceship: easy, outside over land: nope).

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Have a room-temperature superconductor inside the light. There will need to be a moderate-strength electromagnet near any location you intend to use the light in. This does reduce utility outside any developed regions, but makes reasonable sense for a futuristic mansion or ship.

The light will then levitate above the floor, at whatever height and location it is placed, due to how superconductors behave when inside a magnetic field (flux pinning). One advantage of using superconductors is the light will be very stable - due to flux pinning, a magnetically levitated superconducter does not really move around inside a magnetic field unless an external force is applied.

Since the floor is already a large electromagnet, you can power the light via electromagnetic induction assuming you configure the floor to produce a moving magnetic field. This also means that the power source can be as large as necessary, since it is part of the floor infrastucture rather than the light.

As described, this configuration does not follow any given owner, but rather floats wherever it is placed. Since getting the light to float is already taken care of, a basic sensor suite and propulsion system (e.g. an omni-directional air jet) should be sufficient to get the light to follow a given target. A more primitive alternative would be to use some sort of tether.

This solution does have some caveats:

  • The light will not function outside of the magnetic field produced by the electromagnets. Consequently, a fair amount of infrastructure is required to make such a system feasible.
  • Room-temperature superconducters are curently theoretical, although recent developements in suberconductor technology do suggest they may be acheivable in the near(ish) future.
  • Powerfull electromagnets do not play well with magnetic materials or unshielded electronics. If handled properly, this good be a benifit (added security), rather than a detriment.

One other advantage to the electromagnetic floor system is you can use it to levitate and power a wide variety of other devices; it could even be used as the sole means of power distribution for the ship or building that contained it.

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