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Dim blue light can knock electrons out of a metal when bright red light never will.

Physics Facts, sourced to HyperPhysics, Georgia State University.

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If light were only a wave, turning up the brightness would eventually supply enough energy and color would not matter. It does not work that way. Each electron is freed by a single packet of light or by none, and the energy in a packet is set by the color rather than by the brightness. Below a threshold color, no amount of light does anything. Einstein explained this in 1905, and it is the work his Nobel Prize actually cites.

The claim comes from HyperPhysics, Georgia State University.

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