We measure pur as par ( photosynthetically available radation )
Depending on the depth at which a coral or plant is found they have adapted or evolved to use the specific pur at a given depth. With par measured in the nanometer range a 500 to 800 nanometer range yellow, Orange and red region ( closer replicate the sun at a given depth )would be found closer to the surface of the water. As the sun penetrates the water the yellow, Orange and red is filtered out then you have the 400 to 500 nanometer range (blue region) which most of our corals do best under and what looks best to us. As the sun penetrates farther it ends up in the purple region and eventually black with almost no usable light.
So it would depend on the host algae and depth at which a specific coral or plant is found that it has adapted itself or evolved to use a specific pur. ( usable radation )