When an electric current passes through a low-pressure gas confined in an isolated discharge tube, high-energy electrons collide with gas atoms and transfer energy through inelastic collisions. These collisions excite electrons within the atoms to higher quantized energy states. Because electron energy levels are discrete, the excited electrons cannot remain in these unstable states for long. As they relax back to lower energy levels, they emit photons with energies precisely equal to the difference between those energy states (ΔE = hν). The wavelength (and therefore color) of the emitted light depends entirely on the unique electronic structure of the gas. Each element produces a characteristic emission spectrum — a spectral fingerprint — which is why neon glows red-orange, mercury appears blue-violet, and hydrogen emits its distinct pinkish hue. This phenomenon is a direct demonstration of quantum mechanics in action: light is emitted not continuously, but at specific wavelengths d...