The main source of light on Earth is the Sun. Sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the energy used by living things. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence. For example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey.
Tsugumi Ohba, the story writer of Death Note, said that his editor suggested the family name "Yagami" for Light. Ohba said that he did not feel "too concerned" about the meaning of the name (the Kanji for "Yagami" are "night" and "god"); he said that after he created the final scene in the manga he "liked" that the final scene created "deeper significance" in the name, of Kira worshippers worshipping him at night under the light of the moon.
The book centres on the lives of three individuals— the physicist (and serial killer) Michael Kearney, on the verge of a breakthrough in theoretical physics sometime in 1999; Seria Mau Genlicher, the cybernetically-altered female pilot of a "K-ship", and the ex-space pilot and adventurer Ed Chianese. Seria Mau and Ed's stories take place in the year 2400 AD.
The lives of these three individuals are linked in many ways, though most tangibly by the presence of a mysterious creature called The Shrander, who appears in many guises to all three characters throughout the novel (with anagrammatic names of Sandra Shen and Dr. Haends). They are also linked by the Kefahuchi Tract, a space-time anomaly described as "a singularitywithout an event horizon", an object of awe and wonder that has been the ruin of many civilisations attempting to decode its mysteries.