Video narration
Why can dim blue light eject electrons when bright red light cannot? Think of a solar calculator: light transfers energy to electrons, though its mechanism is different. Light arrives as photons. Brightness means more photons per second, not more energy in each photon. A photon's energy depends on frequency: E=hf. Blue light has higher frequency, so its photons carry more energy than red photons. But each material has a minimum energy, its work function. A photon below that threshold cannot eject an electron, no matter how intense the light is. Here's the turn: frequency decides whether an electron can escape. Intensity decides how many escape after the threshold is passed. Above threshold, K_max = hf − φ: higher frequency gives electrons more kinetic energy. So dim blue can eject electrons when its photons clear the threshold, but bright red can fail below it. Brightness cannot energize each red photon.