The phrase tired light was coined for a type of theory that electromagnetic radiation from very distant objects appears more red (wavelengths lengthened or filtered) for reasons other than a Doppler shift due to the Hubble expansion, our current notion of cosmological redshift. When evidence of cosmological expansion was first uncovered, a completely new and radical 20th-century notion, it was natural and necessary to explore alternate hypotheses. The best-known theory of tired light (typically what is meant by the phrase today) was by Felix Zwicky: that scattering along the way resulted in photons of reduced energy, i.e., longer wavelength. However Zwicky also pointed out that this could be expected to cause a blurring of distant objects that was not detected. A number of phenomena independent of longer-wavelength EMR support the notion of cosmological expansion, one of which is cosmological time dilation such as time dilation of distant supernova light curves, which is easily explained by the Hubble expansion.