So, I plan to write a graphic novel that takes place in the 26th century. By then, humans have stopped using the old slugthrowers and have upgraded to something more.....eloquent. I mean, if you're gonna go massacre some alien scum, might as well do it in style.

Enter the Tengellian Arms Manufacturing Co. They have a monopoly on handheld laser weaponry and larger mounted laser cannon turrets. You want a pistol, you go to them! In both cases, lasers heat up gases that turn into plasma.

Tengellian Arms has large contracts with the Terran military, and all military personnel are outfitted with one of their Z-XX67 laser pistols as their sidearms. The Terran military's enemies, a terrorist group known as “Anarchy’s Fists”, also are outfitted with a similar model of gun. I want to make the two sides seem different and split, so I make the Terrans’ lasers fire green, and the AF’s lasers fire red. But this doesn’t make that much logical sense, since they both use a similar model of weaponry, from the same manufacturer.

So, what would be a plausible reason why a manufacturer would make two models of the same weapon different colors?

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Monica Cellio Jun 19 '18 at 3:26

13 Answers 13


For when your "laser" weapon doesn't actually shoot lasers:

In many cases, such as in Star Wars, what people refer to as laser weapons don't actually shoot lasers. In Star Wars, the weapons actually fire plasma. There are some advantages to using plasma over lasers - for one, it's reasonable for a plasma to visible, but a laser is only visible when part of the laser is being deflected by whatever it is passing through (so in space a laser would be invisible except where it hit).

The color that a plasma glows depends on what gas is used to make the plasma. Then the different colors can be explained by using different gasses (you likely don't even have to say what gasses they are using, as the grunts using the weapons might not know). So the reason for the different colors is that the weapons are actually quite flexible in what they can use to produce plasma. The Terrans would be using the gas that is recommended and/or supplied by the weapon manufacturer, while AF does not.

It's up to you to decide what the consequences are of not using the recommended gas. I think the consequences will fall into one of three categories:

  1. The manufacturer has access to a lot of one gas (maybe as a byproduct of the manufacturing proces), while AF has access to a lot of a different gas. There's effectively no difference between them other than their color.
  2. The terrorists found something that increases the effectiveness of the weapons, possibly with tradeoffs. For example, their weapons could be powerful but slightly less accurate.
  3. Due to being more strapped for resources, the terrorists have to use whatever they have available, even though it causes their weapons to be less reliable or less powerful or inferior in some other way.
  • $\begingroup$ Should also mention that lasers even when visible due to passing through a medium would always be seen as a solid beam - you wouldn't see a moving projectile such as those seen in Star Wars. It's light, thus literally moves at light speed, so you wouldn't be able to perceive any motion unless you were moving at near light-speed yourself. The phasers in Star Trek (at least from TNG on) are more accurate in this respect. (I'm pretty sure they thus couldn't use the ship's phasers while travelling at warp speed, but they may have broken that rule a few times...) $\endgroup$ – Darrel Hoffman Jun 17 '18 at 5:21
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    $\begingroup$ As an addition, Plasma loses a ton of heat and thus firepower as it travels through the air, so a containment module is necessary to insulate the plasma. This could be a see-through container like a type of Glass (double-glazed), and the reaction of the gasses with the container gives it its color. Upon a hit the container breaks and works as a miniature shaped-charge as the compressed plasma blows out into whatever broke the container. Different manufacturing processes of the container create different colours. $\endgroup$ – Demigan Jun 17 '18 at 8:47
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    $\begingroup$ @DarrelHoffman : "so you wouldn't be able to perceive any motion unless you were moving at near light-speed yourself" : Actually, you wouldn't be able to perceive any motion even if you were moving at near light-speed yourself. Light travels at the same speed, for any reference not also moving at light speed. Whether you are stationary or moving at 99.99999% of light speed, you would perceive light traveling at the exact same speed. Look up the Michelson-Morley experiment and special relativity. $\endgroup$ – vsz Jun 17 '18 at 18:42
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    $\begingroup$ Rebels on earth are famous for the AK 47, and why is that? Reliability and cheapness. If you live in a cave on the Afghanimoon you might not have the cash and special storage that is required for your fancy "green colour" $\endgroup$ – Borgh Jun 18 '18 at 7:45
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    $\begingroup$ @alice ah, no, it works the other way around. You will appear squished to a pancake (though other effects turn that into a mere rotation), but so will everything else appear to you. Otherwise it would take you longer to get somewhere the faster you traveled. $\endgroup$ – John Dvorak Jun 18 '18 at 15:24

Different safety requirements

Your Terrans, of course, have the most stringent safety requirements in the galaxy. They buy above the board, legally, and check all the boxes necessary before anyone fires a new weapon. On the other hand, a terrorist group is less likely to be concerned with safety checks and standard operating procedures. They buy wholesale from discount merchants who can only be found on desert planets and are lackadaisical at best with their background checks.

Now, there are a couple reasons that the color of light would change in a more questionable model. One reason would be that they're simply older models, and thus less powerful. Green lasers are in general higher wattage and more dangerous than red ones, so perhaps Tengellian Arms has put out a more powerful model recently, leaving only the outdated ones on the black market. Another reason might be degradation of parts within the weapon itself - admittedly a stretch based on how we currently create lasers, but certainly plausible within a sci-fi universe that includes laser weaponry. Finally, perhaps the red lasers are actually the more powerful ones, with a higher intensity or beam width, and the Terrans deem them unsafe for their troops but the anarchists have no such qualms.


Let's talk Physics!

Ok, what is Plasma? Plasma is a very specific state of matter, that is also known as the fourth state of matter. under normal conditions it doesn't exist, and on earth usually is achieved by heating and compressing gases and applying a current. When the current flows through the plasma, it lifts electrons to higher states, which emits light as they bounce back. The wavelength is dependant on the energy gap between the energized and normal state, and thus dependant on the matter that is in plasma state.

Colorful Light!

aka "Luninescense of gases from electron avalance in a discharge tube"

Both Neon and Argon are relatively known examples, because these noble gases are abundantly used in light tubes. Neon is the telltale orange-red, Argon a pale purple, Xenon a blue and Helium as well as Krypton tones of yellow. Hydrogen is a red-purple, deuterium is "sith red", nitrogen a vibrant purple, mercury a bright white-blue. So we can have different glowing plasmas easily. But what about them using the exact same device but for the contents of the gas-tank?!

I found a general number, that one foot of neon light would draw 3.5 to 4 Watts, but couldn't find such numbers for the other gases. But because the gap to the next eectron level slims down the larger the atom is, I expect slightly smaller numbers for all but Helium to achieve luminescense.

And just because everybody loves pictures: Gas Discharge Tubes


But the plasma in neon lights is relatively cold and does not react well to unconfined space. So, the plasma might (also?) get its color from a different source but the gas composition.


There is a different thing people always forget when dealing with plasma, and that is, that its properties are in long stretches a little gaslike, and thus the formulas for gases are used to make very rough estimates. For example $pV=nRT$, the gas law. There is pressure, Volume, number of mols of atoms involved, Gas constant R and finally Temperature1. Combine this with the light emitted by a black body from the Stefan-Boltzman law ($j^*=\sigma T^4$, where $\sigma=5.56\times 10^-8 \frac{\text W}{\text m^2 \text K^4}$), we get this monster:

(1) $\frac{pV}{nR}=T$

(2) $j^*= \sigma T^4 = \sigma (\frac{pV}{nR})^4$

So the result is, that our emitted light spectrum is dependant on the temperature2, which in turn can be modeled via the gas law (to some degree) as being just dependant on pressure and volume. To reach a high temperature, let's say 6000K to get a golden sun orange glowing fireball, we can grab our other properties to look at what we need. Let's say our gun has a chamber of 1 cm² cut area and 5 cm length, so 5cm³ volume ($5 \times 10^{-6}\text m^3$).

$\frac {T R} V = \frac p n$

Our Pressures are pretty high if we want to conserve ammo: 1 mol of gas under 1 atmosphere is 22.4 liters - or if we have a box with 1 m² area, it stacks about 22.4 mm high, about a finger wide or almost an inch. A standard gas container uses about 200 bar and stores 200 liters of standard condition gas in 1 liter. Assuming a nice half liter gas tank and 200 bar storage pressure, we can carry around the number of atoms usually in 100 liters of gas at standard pressure. That's about 4.46 mol in the bottle. NOW comes the tricky part: for each shot, we will need gas, so we need to portion it. Let's assume for simplicity that we have 111 shots of 0.04 mol3. Then our pressure would need to be an astonishing $399.072\ \text{MPa}$ 4.

And, because pictures: pick your temperature and luminosity from the Hertzsprung Russel Diagram for possible values.



Yes, it is certainly possible to color your laser-heated plasma bolts to your liking using two screws: the gas used as plasma-precursor and the temperature of the plasma itself. To change the plasma temperature, one could directly assault the issiue of the temperature by using more power on the lasers, or one could alter the gas flow per shot, indirectly altering temperature via the changed pressure(1). And the temperature results in the color of light emission, because of the properties of a black body.

Tuning your plasma color

So, to get other plasma colors using the same base weapon, one could do this:

  1. Use a different gas composition to turn into plasma.
  2. Bore open the containment cylinder to lessen pressure and lower temperature for a more red look - and maybe safety reasons.
  3. Set the valve for the shots to be less open for more shots - and a more red look.
  4. Open the valve more for less shots but a blue style and the risk of blowing the gun in your hand.
  5. Exchange the heating lasers for more powerful ones for more blue.

1 - There is a different notation using $pV=Nk_BT$ with N being the absolute number and kB the Boltzman constant, but both are mathematically aequivalent.

2 - This is not taking into account anything BUT light to transfer energy away. Also, there would be more to this formula - I use the simplified version over all the spectrum here, not the wavelength specific one, that is material dependant.

3 - Let's ignore that the work to remove a set portion of gas from a container is pressure differential dependent. It is easier to let a set amount out of a high-pressure container than to get the same amount from a lower pressure container.

4 - With pressures like that I would not want to hold that gun in my hand. CERN struggles to build up those pressures in their accelerators. And they use more temperature even.

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    $\begingroup$ So a fighter with a low budget might dial down his laser phaser gun from "all of the energy" to "a reasonable amount of energy" to save the battery, which would change the color? $\endgroup$ – SPavel Jun 18 '18 at 17:15
  • $\begingroup$ @SPavel a little, yes. Also, they might save more of the gas for the plasma by dialing that ammount down - both reduce the heat of the plasma bolt for more shots. $\endgroup$ – Trish Jun 18 '18 at 21:59
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    $\begingroup$ Now that's an answer. BTW, don't discount barrel wear. The lower temperatures would likely cause less barrel erosion. So now, there are three savings for the budget minded. The lower temps might also be good when you are fighting in areas where blowing through walls/bulkheads would be bad. $\endgroup$ – ShadoCat Jun 19 '18 at 20:09
  • $\begingroup$ Fighters might also take into account the armor worn by their opponents. Do you want to try to burn straight through and cause internal damage, do you want to knock them with kinetic energy and break bones without penetrating, do you want to heat their whole suit to cook them alive, or do you want to create an em pulse at the destination, shutting down their systems? Ammunition with different effects might have different light and your choice of effect may depend on who your opponent is. $\endgroup$ – Muuski Jun 13 '19 at 23:51
  • $\begingroup$ Speed and cohesion of the plasma are not parameters that influence the color of a gas, temperature and pressure of the gas are. $\endgroup$ – Trish Jun 14 '19 at 4:41

Very simply because they use different wavelengths, and thus have different interaction with the target.

enter image description here

Think of the wavelength like the bullet of a gun or a rifle: sometimes you can use hollow head, sometimes you can use rubber head, sometimes some other head, according to the type of interaction you want between the bullet and the target.

All bullets are manufactured by the same manufacturer, and also the gun/rifle. Yet they have different features.

enter image description here

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    $\begingroup$ The OP would still need to explain why the Terran military and the AF have different (weapon) needs when fighting each other on the same battleground. $\endgroup$ – user3106 Jun 18 '18 at 9:57
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    $\begingroup$ @JanDoggen, maybe one target is more sensitive to blue and the other to red... $\endgroup$ – L.Dutch - Reinstate Monica Jun 18 '18 at 10:06
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    $\begingroup$ @L.Dutch "They're wearing blue armour! Quick, switch to red beams!" $\endgroup$ – DaveMongoose Jun 19 '18 at 9:20

The answers above provide some great considerations, I would just also add that in battle, it is important to make quick determinations of friend or foe. Just like armies try to use uniforms of different colors, the Terrans and the anarchists could be using the laser colors for the same purpose.

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    $\begingroup$ In this case, a tactic the Freedom Fighters will undoubtedly use is some kind of (illegal!) switch that allows them to fire a more Terran Federation friendly colour of phlazer. Pretend like they're friends so an enemy detachment won't try to kill them right away. Then blammo!!, switch over to their accustomed and sinister hue of red for the kill! $\endgroup$ – elemtilas Jun 17 '18 at 5:23
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    $\begingroup$ @elemtilas: Actually, I plan for a scene kinda similar to that. The main character has just infiltrated the freedom fighters, but ruins the whole show. Just by using his pistol. $\endgroup$ – Jasper R. Jun 17 '18 at 6:00
  • $\begingroup$ Oups!! An oversight to ruin one's day. $\endgroup$ – elemtilas Jun 17 '18 at 16:52
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    $\begingroup$ Well that leads to the idea that you just need to have an agent quietly swap out the weapons of some key personnel to plant some doubt and paranoia. $\endgroup$ – Michael Richardson Jun 18 '18 at 15:48

Weapon Cosmetics

All other answers are quite scientific, but mine is going to be fully fictional.

Your manufacturer might sell skins or modifications for their weapons separately as an extension. This is not a very strange idea, weapon cosmetics is the main revenue for many multiplayer games(CS:GO, DotA). People pay for cosmetics that doesn't change anything on the weapon in terms of effectiveness but makes it look cooler.

While your unmodified laser weapons shoot red, the army orders ones in green , so that they provide better camouflage on forests. They also have exclusive deal with the manufacturer so no other party can use the green laser instead of the army.

Your terrorists are now left with red unmodified laser. This system also gives you an opportunity to add more colors to your novel. You can make your terrorist generals use more modified skins like black lasers or purple. You can also make your default laser color yellow, and make terrorist turn it to red by modifying it so that they have a signature lase sign. This might also be a plot point. Similar to red and blue lightsabers in Star Wars.

  • $\begingroup$ Cosmetic and slightly useless attachments are sold and used in real life too. (Just a sort of a did ya know) $\endgroup$ – The Mattbat999 Jun 18 '18 at 1:27
  • $\begingroup$ How would you have a black laser? Black is the absence of light! (: $\endgroup$ – SilverWolf - Reinstate Monica Jun 18 '18 at 15:23
  • $\begingroup$ @seaturtle yes, that makes sense, but I don't know maybe generals are using rainbow colored lasers. $\endgroup$ – atakanyenel Jun 18 '18 at 16:31
  • $\begingroup$ @seaturtle - maybe more like a near-UV laser? Or infared? $\endgroup$ – IronEagle Jun 18 '18 at 21:17
  • $\begingroup$ I want mine to say "pew pew" when I fire it. $\endgroup$ – Draco18s no longer trusts SE Jun 19 '18 at 2:11

They're selling the rebels the "seconds", the stock that doesn't pass all the Quality Control tests. The good stock has pure lasing stock uncontaminated by traces of the factory atmosphere and produces a nice bright green, or blue or whatsoever you please, flash when you pull the trigger, the seconds stock has oxygen contamination and is far more variable in it's output but tends to be more (your choice of colour here). The company officially writes off all it's second class lasing stock as a dead loss but off the books they create finished product, using equally written off body and power components and supply the black market with second rate, but serviceable, weapons.


I will admit that I don't like stories that break the suspension of disbelief. One visible company selling all the weaponry seems wrong to me. I would think it would be something closer to what the US detergent market is like, where there are really only a very few companies, but they break themselves up into multiple brands to make it look like there is real competition.

So one sub-brand could sell only to the military and another could be marketed to civilians. They would be different colors to distinguish the brand. The military ones might be more powerful, and perhaps at least one of the civilian brands would be more durable for use as hunting weapons.

I would also think that the terrorists would have some military weaponry. Usually freedom-fighters/terrorists tend to be less picky about how they acquire their weapons, at least in fiction. And many military units tend to be involved in black markets. So I'd expect to see the terrorist have at least a few military weapons. Likewise, I'd expect some improvised weapons and perhaps some old (or new) projectile weapons because they are probably easier to make than the plasma weapons.


Make the difference in colors be a side effect of another feature, then explain why each faction favors a certain plasma type.

Maybe red is better for armor or force field penetration, but green is better for unarmored or lightly armored targets, because it moves faster and deals more damage. AF would choose red, because the military has heavy armor or uses force fields. The military would choose green, because AF isn't so heavily armored.

Maybe one color is lethal and the other isn't, and only one faction is shooting to kill, the other wants to incapacitate and capture its opponents.

Maybe red plasma is more powerful, but banned by international law. AF, of course, doesn't care about that.

In general, find a way to make each faction want to use one or another.

  • $\begingroup$ Welcome to Worldbuilding, J. Brennan! If you have a moment please take the tour and visit the help center to learn more about the site. You may also find Worldbuilding Meta and The Sandbox (both of which require 5 rep to post on) useful. Have fun! $\endgroup$ – FoxElemental Jun 18 '18 at 17:19

Forensic ballistics

In the future maybe we don't shoot bullets, and it's a bit of a conundrum since, if you've ever watched CSI or some serious-murder-police-procedural, bullets can be matched to the gun that fired them. Presumably, each gun is unique, or unique-enough that two murder suspects wouldn't leave the same marks.

You could recreate that in a plasma rifle by altering the composition of said plasma ever so slightly, which would give it different colours (maybe not always strictly visible to the human eye) and which might leave unique (or unique-enough) chemical marks on what they hit. Of course, that would heavily depend on what the underlying technology is.

Rights guns and wrong hands

You might sell guns to the military, the police or civilians. More than that, you might sell guns to multiple militaries, multiple police forces, in multiple jurisdiction, etc. Having distinct colours (e.g. green for military, blue for police, red for civilians) would help know who is shooting.

A practical application is if the military gets shot at with weapons that fire green, then they might rightfully go ask the manufacturer what the hell. Or it might be the sign somebody is stealing their guns. Or better yet, instead of green the rebels shoot yellow, which is the colour assigned to another nation's military. So many possibilities for drama.

Out of universe

Rule of cool. Alternatively, colour-coded for your convenience. A multicoloured laser show will look better, and it will help the audience identify who is who. It's unlikely people would question it either. Star Wars gets away with different-coloured blasters with no explaination, no reason you wouldn't either.


To be really underhanded, they could fire "polarized plasma" that appears one color from behind and another from in front

  • $\begingroup$ Welcome to Worldbuilding, rhewe! If you have a moment please take the tour and visit the help center to learn more about the site. You may also find Worldbuilding Meta and The Sandbox (both of which require 5 rep to post on) useful. Have fun! $\endgroup$ – FoxElemental Jun 18 '18 at 20:08
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    $\begingroup$ Welcome to Worldbuilding. Just so you know, this answer is a bit short. When answering, you should elaborate a bit more and say why they would want to do this (what advantage it would give them) and, if you know, how they would do it. Also, the question was why or how question and you didn't answer those. $\endgroup$ – ShadoCat Jun 18 '18 at 20:43
  • $\begingroup$ @ShadoCat, are you sure? This appears to be a clever solution to the problem. $\endgroup$ – JBH Jun 19 '18 at 2:45
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    $\begingroup$ @ShadoCat, oh, no doubt! Like I said, the idea of using polarization to justify two colors was clever. You're absolutely right that it would need a good explanation. (Then again, Jasper never tagged the question science-based. The enemy using an aftershave made from fairy dust that shifts the frequency of discharged weapons would be as good an answer. 😆) $\endgroup$ – JBH Jun 19 '18 at 20:16
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    $\begingroup$ @JBH, so, post that as an answer. Just, please, explain it a bit. :-) $\endgroup$ – ShadoCat Jun 19 '18 at 20:20

In the real world there are multiple colours of tracer bullets

Notably the US (and Nato forces in general) favour strontium based red tracers, while russia and china favour barium Green.

So in a hypothetical WW3 we may well encounter red vs green tracer fire!
In fact, this apparently happened during the vietnam war as the Viet-Cong were being supplied with surplus weapons and particularly Green tracer ammunition from the soviets and chinese at the time.

Being able to instantly know that a shot came from the enemy because it isn't your own colour is very useful, so your two factions may well dope their plasma fuel with secondary gases to tint the shot.


Why would the armies want different colors?

So you can see who's on your side. Like a uniform, you can know who to shoot without asking for ID first. Yes, there will be instances of infiltration, but that's just part of the story building.

Why would the manufacturer make different colors?

Because selling to both sides gives double profit. Arms dealers make huge amounts of money supplying both sides of a war.

Alternatively, maybe the tech means you can choose on the gun what color/power/spread the projectiles are. Then the manufacturer can look innocent, while each side can configure their own colors/standards.


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