Common rockweed, which normally appears greenish-brown, is bright red and green when exposed to ultraviolet light at low tide off Fidalgo Head near Anacortes, Washington. The glow is fluorescence, a type of photoluminescence, in which certain chemicals absorb light that is invisible to human eyes and emit some of it at a different wavelength that we can see. This scene was captured under black light at Sunset Beach in Washington Park.
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