A few thousand years ago, a mysterious and powerful alien race decided to test the limits of evolution and adaptation. After careful observation, the aliens decided humans would be the perfect subjects for this experiment.
One thousand humans were abducted from Earth for these experiments, but only half survived being injected with Lutio, a solution created to accelerate evolution and mutations. The survivors were split into 5 testing groups. Group B was placed on Ellula, an electrically charged planet of darkness orbiting a tiny star.
Finding it difficult to navigate the dark planet, Group B eventually mutated and developed light sources on their own bodies - from light bulbs to bio-luminescent skin, soon all of Group B was shining. However, producing light takes a lot of energy, and there was little food to be found on Ellula.
After a few generations, another mutation appeared. Some of Group B began to notice a strange energy surging through them when they lay flat against the planet's surface. Starting as a warmth in their lower back, they could lie down for a few hours and re-energise. This strange energy also sated their hunger. Eventually, Group B evolved tails they could stick into the planet's soil and recharge themselves.
Having solved their food and light issues, Group B began to build their own society on Ellula. Calling themselves Bulbettes, the species progressed similarly to humans. Currently, Bulbettes are slightly more advanced than humans and are capable of minor space travel. Their first destination: Earth.
Physiology 
A few thousand years ago, a mysterious and powerful alien race decided to test the limits of evolution and adaptation. After careful observation, the aliens decided humans would be the perfect subjects for this experiment.
Bulbettes are almost identical to humans in physiology, with similar lifespans and reproduction. However, Bulbettes have a few extra quirks outside of their light sources and power cable tails.
At the base of a Bulbette's tail is an organ called the converter. This organ transforms electrical energy that travels through the tail into chemical energy to be used throughout the body. Bulbettes also evolved to have stronger teeth and stomach acid than humans, as well as some resistance to poisons. This adaptation was in response to Ellula's scarce food being tough and often poisonous. As a result, Bulbettes can easily digest bark, bones, and fur.
Bulbettes don't need to sleep or eat, though they can often be found doing these things. Bulbettes that don't eat need to drink more water than the average human, as they need to replace the water that would normally come from food. Bulbettes can perform sedentary tasks while charging, such as reading and writing, and an average Bulbette needs to charge for 4 hours out of 24. Bulbettes can sometimes overcharge to gain an energy boost, but consistent overcharging can dim a Bulbette's light source.
Mythology 
Firehawk, a Bulbette with a crown of flames and wings of a phoenix. One of the first evolvers, he was a powerful man who defended a small tribe of lightless Bulbettes under the guidance of Cassandra.
Cassandra, a Bulbette with limbs of glowing crystal and all-seeing crystal eyes. Leader of the lightless tribe, Cassandra was said to know all that was and all that would be.
As the legends tell it, a larger tribe of Bulbettes feared the strange light sources the two possessed and slaughtered their tribe. Filled with anguish and rage, Firehawk spread his great wings and flew Cassandra to Elluna, Ellula's moon.
Most modern Bulbettes don't believe in the old legends, but some Bulbettes swear that during an eclipse you can see a pair of strange lights on Elluna.
Hybrids 
There is no taboo against breeding with other species in Bulbette culture, so hybrids between Bulbettes and other species are fairly common. Bulbettes are limited to reproducing with other humanoid species.
Hybrid Bulbettes don't develop a converter organ, and so hybrids are unable to recharge through electrical means. To compensate, Hybrid Bulbettes need to eat about two times the normal caloric intake of a similarly sized human. Hybrid Bulbettes retain their light source(s) and power cable tail, though the tail is non-functional.
Puberty 
Bulbettes experience puberty similarly to humans. Though Bulbettes are born with their power cable tail, which grows in proportion to the Bulbette, they are not born with their light source.
Light sources that protrude from the skin, such as bare bulbs and fairy lights, begin as small freckles, then develop into moles that progressively protrude from the skin more as time goes on. The bulb of these light sources develops almost like a balloon - first it is small and opaque, then as it grows larger it becomes more and more transparent.
Light sources that are one with the skin, such as lava lamps and screen wraps, act similarly to a painless sunburn. Some Bulbettes experience only a couple weeks of peeling, while some take longer.