But doubts remained. In 1900, Max Planck found that the way heat radiated from a hot object could be explained only if it was emitted in tiny packets of energy that he called quanta, from the Latin for 'how much'. In 1902, Philipp Lenard discovered the photo-electric effect now exploited in solar cells. He found that when light strikes certain metals, electrons are released. Later Albert Einstein suggested the photo-electric effect can be explained if light is tiny energy packets like quanta.
Most scientists now accept light is indeed energy packets, which they call photons.
Light from electrons Light comes from atoms. When an atom is energized by, say, an electric spark, it becomes excited and an electron may be pushed further out from the nucleus. It's a bit like stretching a rubber band. Then, as if the rubber band is released, the electron slips back in again, firing off a photon as it goes. The wavelength of the photon fired off depends on the size of the electron's jump as it returns to its original level.