How realistic are living creatures whose skin burns when exposed to light?

Question

I started playing one of the Metro games, and one of the common enemies is an armor plated Spider the size of a small dog that your character's flashlight causes its armor to boil as if the light is acid. Eventually I took a break from this, walked past the TV and the movie Pitch Black was starting. It is set on a desert world inhabited by these bug like creatures larger than humans, and have the same trait of being physically injured by light. In both instances, too much exposure to light seems to be fatal to these creatures, with the Metro case being about 10-20 seconds being enough to kill them.

Having coincidentally seeing both of these instances in such a short time span I got to thinking. How realistic is the general idea of a creature which when exposed to light of even a flashlight causes its skin to burn as if it's on fire, leading to the creature's death in a short time span? If not a flashlight, then more powerful or special sources are still acceptable, such as maybe UV lights.

It would be preferable if a human were exposed to the same conditions that would be near certain death to the creature, the human would be mostly unscathed, but the line is drawn so long as a human is at least more likely to survive the said exposure than not. The ability to weaponize the light is of a high priority here, so we don't want to turn on a special flashlight and have it effectively become a suicide bomb unless that is the only way for this creature to exist.

Answer 1

I'll give a conditional 'yes it is realistic' answer to this, but very conditional. The key part here is you don't actually need to fuel the reaction with the energy of light, you simply need light to initiate the reaction and the resulting compound to react with something else.

For example, hydrogen peroxide will degrade to water and oxygen when exposed to light (admittedly slower process). We know the reaction of some metals with water is relatively aggressive to outright explosive. Had this creature be composed of, lets say potassium and hydrogen peroxide, then the breakdown of hydrogen peroxide into water and the then reaction of water and potassium could give a boiling/acid texture to the outside of the creature. Mind you, in pitch black the giant rainstorm woulds produced some pretty fireworks if these creatures were composed of potassium. How exactly a creature would evolve to contain something so unstable is a bit of a mystery as well.

More research needed, but I do believe there is some feasibility in light initiating a reaction that cascades into something much greater from there.

edit: Try a second one. Silver iodide converts to metallic silver and releases the iodine in the presence of light (can be used in photography). Ammonia plus Iodine will create nitrogen triiodide, which gives off a purple smoke.

Ya I'm reaching. Kinda fun, but reaching.

second edit:

I think I might have the best option I can find here...silver bromine. Once again, you need to have a creature with a nearly silly mix of chemicals in it's body, but silver bromide reacts with light, releasing the bromine which could react with aluminum or a few others to cause a reaction. Why exactly a creature would be composed of something this unstable would be another question

I guess this post has become a very long winded way of saying theres less than 0.000001% chance of this feasibly happening.

Answer 2

Let's consider the fact that the Sun is actually harmful to most creatures, given the right conditions. Humans around the world get sunburned every day, and millions contract skin cancer every year as a result of UV exposure.

What is a sunburn? Though we often don't think of it this way, it's actually a radiation burn that causes cellular damage. The Sun is constantly bombarding us with deadly ultraviolet radiation, and the Earth's ozone layer filters out most of this harmful light. But what about the radiation that makes it through? The vast majority of it is dissipated by melanin, the pigment that gives our skin color. People with darker skin tones - that is to say, more melanin - have been found to be able to handle sun exposure better than fair-skinned people, who tend to burn more easily. But what if someone didn't have any melanin at all?

That condition is known as albinism, a disorder that a person or animal is born with and is passed down genetically. In albinos, even the irises of the eyes lack pigment, which is why they appear red: you are seeing straight through to the retina. Normally, the iris contracts and expands to let more or less light in - this is why your pupils appear dilated in dim light, but much smaller in bright light. In the case of an albino's iris, since it is transparent, it cannot effectively block the light entering the eye. Because of this, albinos tend to have difficulty seeing in bright light, and many even experience discomfort or pain.

Answer 3

The lasers used in surgery (particularly eye surgery) uses a UV frequency that dissolves flesh efficiently without causing heat in the neighboring tissue.

The ultraviolet light from an excimer laser is well absorbed by biological matter and organic compounds. Rather than burning or cutting material, the excimer laser adds enough energy to disrupt the molecular bonds of the surface tissue, which effectively disintegrates into the air in a tightly controlled manner through ablation rather than burning.

The outer skin layer of a creature might be sensitive in this manner, so a flashlight-like device is especially distructive with surprisingly little power, if it puts all the energy into the target wavelength like lasers (and LEDs) do.

The thing is that UV is right on tge edge where photons have enough energy to affect chemical bonds directly at our Eartly temperature and composition. That's not universal though, as we manged to get photosensitive proteins for use in our eyes. So it’s at least chemically possible that the skin of some alien will have some protein in it that’s sensitive to what we call “visible” light.

In fact, one of my early (affordable) LED flashlights was a torquise LED. Emitting a monochromatic beam uses far less power, especially when it uses the color that our eyes are most sensitive too!

Answer 4

For a creature to be hurt by any light, this is very unrealistic. Think about it - a large flashlight is typically powered by a couple batteries. If you had a flashlight that used 4 D-cell batteries in series, that gets you 6 Volts. You can (though I'd suggest watching a video of someone else doing it rather than trying it yourself) put a 9 volt battery on your tongue without serious harm. Why would transforming that energy into another form suddenly make it considerably more dangerous?

Given that not much energy is being delivered by such light, in order for the light to be harmful the creature's skin would have to be highly reactive to light. However, if it's highly reactive to any light that means the chemicals must be quite unstable, meaning they'd decay much faster and require a lot more energy to maintain. It's possible that you could contrive some situation in which this would actually be an evolutionary advantage, but it would have to be a very unusual situation.

Answer 5

Extremely unrealistic.

To an extremely good first approximation all life on Earth is powered by the sun and it's very, very likely that this will be true of all life we ever find for the very simply reason that it's difficult to imagine another bio-available powersource that could take its place.

All plant life must exist in the sunlight, so it follows that for most animal life they would need to also be able to exist in sunlight or they're cut off from their food source for half of the time. This is especially true for earlier animal life since they will lack complex behavioural adaptations required to hide completely from the sunlight.

So we have life evolved from sunlight-capable life, and competing with sunlight-capable life, that not only adapts to living in the dark but somehow evolves to be harmed by light. To explode, as you suggest, this needs to go even further have a outer covering that is highly volatile in light but outer coverings benefit from being inert because this gives the most protection. I cannot conceive of any conditions where explody-reaction-to-light would be evolutionarily favoured over not-explody-reaction-to-light.

Answer 6

There are people who literally cannot go out into sunlight without receiving severe damage to their skin with severe sunburns or increased cancer risk, which can lead to death. The disease for this is called Xeroderma pigmentosum.

There have been several documentaries on this disease, as well as the focus of a few novels. Maybe not as severe as Metro's creatures, but still very severe.