Zooxanthellae use a number of mechanisms not available to plants to harness light energy from other portions of the spectrum. These include, but are not limited to UV-A rays, and are responsible for the rich coloration you see on your corals.
If we were only concerned with the PPFD over the PAR region, then we might be tempted to think that 6500k Iwasakis (189 PPFD @ PAR) are more desirable than 20k Radiums (85 PPFD @ PAR). Try it out for yourself, and you'd find that the corals under the Iwasakis generate xanthophyll pigments to protect themselves from the heat transmitted by higher wavelengths. These give off a rust brown color however, and we tend not to prefer this "look" on our corals. (Though do use lower temperature bulbs on the grounds that the corals receive more PAR light.)
This is why when I argue that DE bulbs generally give off more light, I only speak of raw intensity. Its final effect on coral growth, presentation, or other subjective visual tastes are a completely separate matter to me.
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