Solar LED spotlights for outdoor gardens: When atoms in the solar cell approach each other, sp-mixed orbits are formed (one 3s orbit and three 3p tracks form a combined orbit). Covalent bond formation is formed between adjacent atomic orbitals, and the energy band is as shown in country 2c. Four bonding orbitals form an upper energy band, and four anti-bonding orbitals form a lower energy band. The result of this is that there is a band of electrons between the upper and lower energy bands. Since the four outer electrons possessed by the S source occupy the low energy lower energy band, the upper energy band is empty. Even if the electrons in the lower band are accelerated by the electric field and the energy is increased, since there is no electron in the band, no current can be formed. Thus, pure silicon is an insulator at 70K.