Sunlight Mimicking LEDs

[caters]

I was thinking about my aliens and their generation ship. I did a lot of research on light in general as well as sunlight in particular. Since the aliens are moving away from the sun and facing away from the sun and towards the outer planets when they start their trip with the humans in space, that already dramatically decreases the amount of sunlight that reaches them. But that intensity goes down with the square of the distance. So if you go twice as far from the light source the light source will be 4 times dimmer and if you go 3 times as far the light source will be 9 times dimmer, etc. It eventually gets to a point where it is not visible anymore because only individual photons are reaching you.

This dimming as you go further until you can't see it is why I thought of having, at least in some rooms, sunlight-mimicking LEDs

So I did some research on LEDs and it turns out that different LEDs need different voltages to work. An infrared LED needs less than 1.6 volts so it could easily be powered by a AA battery(or any 1.5 volt battery for that matter). Ultraviolet LEDs on the other hand need 3 to 4.1 volts depending on the type of ultraviolet LED which is equivalent to 2-3 AA batteries.

Then I did some research on how much sunlight reaches the surface and it turns out to roughly be in these proportions:

53% infrared
44% visible
3% ultraviolet

And I did some more research on ultraviolet light and it turns out that no UVC reaches the surface, it is all absorbed by the time it reaches the stratosphere. Of the UV that does reach the surface, it is in roughly these proportions:

95% UVA
5% UVB

So I figured that the aliens should have lightbulbs with lots of LEDs in them(like thousands) so that they can get the LEDs in roughly those proportions and as close as possible to evenly distributed. Of course that won't be a problem with the infrared and visible light. It is really the ultraviolet that they have to worry about getting evenly distributed.

And I also figured that these LEDs should vary in duration and intensity over a 24 hour period to mimic the day-night cycle.

Infrared and Ultraviolet LEDs should always be on and be at their lowest intensities at night. Visible light LEDs should be off at night and be on at varying intensities throughout the 2 twilights(morning and evening twilight) and be at their highest intensities after morning twilight and before evening twilight.

Infrared should rise in intensity during morning twilight and lower in intensity during evening twilight and also be at its highest intensity at the same time the visible light is at its highest intensity.

Ultraviolet should spike up during morning twilight and then stabilize until midmorning when it should spike up again and then stabilize. When it is late afternoon/early evening the ultraviolet should spike back down and stabilize until the end of evening twilight when it should spike back down to night intensity.

With visible light it is a bit more complicated but basically, all the rainbow colors should be off at night and then as morning twilight starts the red LEDs should turn on first, closely followed by orange, yellow, green, and blue. Purple should be the very last light to turn on and since it only increases the intensity of already white light, it can rise in intensity slower than the other colors.

Anyway, what do you think about having these sunlight-mimicking LEDs on the generation ship?

[Moontanman]

27 minutes ago, caters said:

I was thinking about my aliens and their generation ship. I did a lot of research on light in general as well as sunlight in particular. Since the aliens are moving away from the sun and facing away from the sun and towards the outer planets when they start their trip with the humans in space, that already dramatically decreases the amount of sunlight that reaches them. But that intensity goes down with the square of the distance. So if you go twice as far from the light source the light source will be 4 times dimmer and if you go 3 times as far the light source will be 9 times dimmer, etc. It eventually gets to a point where it is not visible anymore because only individual photons are reaching you.

This dimming as you go further until you can't see it is why I thought of having, at least in some rooms, sunlight-mimicking LEDs

So I did some research on LEDs and it turns out that different LEDs need different voltages to work. An infrared LED needs less than 1.6 volts so it could easily be powered by a AA battery(or any 1.5 volt battery for that matter). Ultraviolet LEDs on the other hand need 3 to 4.1 volts depending on the type of ultraviolet LED which is equivalent to 2-3 AA batteries.

Then I did some research on how much sunlight reaches the surface and it turns out to roughly be in these proportions:

53% infrared
44% visible
3% ultraviolet

And I did some more research on ultraviolet light and it turns out that no UVC reaches the surface, it is all absorbed by the time it reaches the stratosphere. Of the UV that does reach the surface, it is in roughly these proportions:

95% UVA
5% UVB

So I figured that the aliens should have lightbulbs with lots of LEDs in them(like thousands) so that they can get the LEDs in roughly those proportions and as close as possible to evenly distributed. Of course that won't be a problem with the infrared and visible light. It is really the ultraviolet that they have to worry about getting evenly distributed.

And I also figured that these LEDs should vary in duration and intensity over a 24 hour period to mimic the day-night cycle.

Infrared and Ultraviolet LEDs should always be on and be at their lowest intensities at night. Visible light LEDs should be off at night and be on at varying intensities throughout the 2 twilights(morning and evening twilight) and be at their highest intensities after morning twilight and before evening twilight.

Infrared should rise in intensity during morning twilight and lower in intensity during evening twilight and also be at its highest intensity at the same time the visible light is at its highest intensity.

Ultraviolet should spike up during morning twilight and then stabilize until midmorning when it should spike up again and then stabilize. When it is late afternoon/early evening the ultraviolet should spike back down and stabilize until the end of evening twilight when it should spike back down to night intensity.

With visible light it is a bit more complicated but basically, all the rainbow colors should be off at night and then as morning twilight starts the red LEDs should turn on first, closely followed by orange, yellow, green, and blue. Purple should be the very last light to turn on and since it only increases the intensity of already white light, it can rise in intensity slower than the other colors.

Anyway, what do you think about having these sunlight-mimicking LEDs on the generation ship?

Light cycles are important for health and plant growth, red and blue light are most important for plant growth but paradoxically it's not day length that determines plant growth it's the length of darkness.

Let's say, for example, your spaceship is a rotating cylinder or torus, plant growth could be maximized by using 24 hours of light and 12 hours of darkness. It's the length of the night that determines things like blooming and growth. LEDs would be a good way to illuminate rooms and such but a more powerful light source would be needed for internal illumination of the interior of the ship if you want to make it resemble an O'neill cylinder. controlled fusion power would almost certainly be necessary for power but once you have fusion many possibilities open up.

A full spectrum is not necessary for plants or to trigger biological systems in animals. But it would be easier on the human eye and if you have the power to spare there is no reason not to include all the spectrum that is reasonable.

Infrared would probably need to be minimized to reduce heat, in space getting rid of excess heat is a bigger problem that staying warm, and UV isn't necessary since the vitamins it creates can be eaten in our food. I would think that UV B could be eliminated completely and UV A minimized.

The imitation of dusk and dawn is probably important to some plants and animals and would be easy to do anyway. 

Edited August 11, 2017 by Moontanman

[Externet]

English... if the thread title was, instead, LEDs mimicking sunlight ; would it have the same meaning ?  Better ?  Worse ?

[caters]

30 minutes ago, Externet said:

English... if the thread title was, instead, LEDs mimicking sunlight ; would it have the same meaning ?  Better ?  Worse ?

I am pretty sure it would have the same meaning.

[John Cuthber]

It's the same  in English.

Much the same issue applies  to "a man eating fish" which is a long standing joke.

[koti]

Is this for a book? If yes, why would you want to confine yourself to semiconductors (LED's) when you can make this so much more interesting?
High Intensity Discharge (HID's) offer the most potent light source as far as mimicking sun (well actually it's not mimicking, its actually a tiny sun as far as light emitting goes) color and surface brightness goes. LED's are very energy efficient but the sheer power of a HiD is impressive and when modified with some scifi whoomp it might be cool. For one, HiD's offer unprecedented surface brightness, this means that the light source is a tiny lightning which enables the beam to travel further (for search lights) as opposed to big, clunky LED's which have to resort to aspheric reflectors for the same beam distance. Why not make it a hypothetical "Quantum Plasma Discharge" (QPD) source of light where an incredibly tiny glowing plasma is controlled by precise magnetic fields changing it's size, emitting pattern, even alter the radiation type emitted according to need. As a power source, you could make it a tiny, cold fusion reactor with energy efficiency of say 60% burning micro grams of matter per month. That sounds to me like a source of light more worthy of an advanced alien species than crappy semi-conductors we use here on earth. Then again, I'm a flashlight freak so my ideas might be too progressive even for aliens

Here's a ~15 thousand dollar flashlight, it never went into production because of high production costs, there is one working prototype in Russia. It might give you some additional ideas for crazy light sources:

 

Edited August 13, 2017 by koti

[caters]

The thing that would worry me about a quantum mechanical sunlight source is waste energy. I mean the sun produces energy in pretty much the entire EM spectrum from radio waves to gamma rays. Not only that but the sun is the strongest radio source in the sky because of its mass and relatively close distance to us.

Radio waves and microwaves would be just a waste of energy that could have been used to produce infrared, visible, and UV light.

X rays, UVC, and gamma rays would be an extreme waste of energy but not only that but they are much more carcinogenic than UVB and UVA.

UVC has a wavelength between 280 and 100 nm. This is energetic enough to age UV resistant plastics, kill bacteria and viruses, and if a human is exposed to it, it can cause:

• Rapid sunburn
• Skin cancer
• Inflamed cornea
• Temporary or permanent vision loss, even blindness
• Damage to the retina

UVC exposure has a maximum time of 8 hours before it is considered unsafe due to these skin and eye injuries. And there is no doubt that the humans on the generation ship would get more than 8 hours of exposure.

However, UVB is essential for life. 10-15 minutes of exposure can produce up to 20,000 IU of vitamin D. And UVB can be used to treat some conditions like:

• Jaundice
• Rickets
• Psoriasis
• Eczema
• Vitiligo
• Atopic dermatitis
• Scleroderma

And infrared is basically heat so it would help the humans stay warm.

X rays as background radiation or as just a plain X ray have a 1 in 1,000,000 lifetime cancer risk but at the doses for CT and Fluoroscopy, it can easily be 1 in 1,000 lifetime cancer risk. Not only that but if the X rays are not shielded it can cause radiation burns which can deform you. This is way worse than the sunburn from UV.

Gamma rays are even worse than this. Gamma rays can cause radiation poisoning where no matter how the person is treated, they will inevitably die from the radiation. And a bit ironically, high dose damage is easier for the body to repair than low dose damage.

 

So there would have to be a way to restrict the frequencies of light that are emitted to infrared, visible, UVA, and UVB. Lower than this and the energy is just a waste. Higher and cancer, burns, and poisoning are going to have a much higher chance of occurring. The only way I can think of to restrict the radiation emitted to this narrow range is to not use a source of lower or higher energy radiation. LEDs are an easy way to avoid this waste energy and medical risk.