Cri - color rendering idex - is basically a scale of how "true" to natural light that bulb/ led will make colors appear to our eyes. Typically a higher cri is going to have higher strength waves on the red end of the spectrum. The stronger reds is a bonus on higher cri but for me personally, 80 cri is usually the most "appealing" rendering of what I'm looking at. Kind of an eye of the beholder type thing.
Where the reds really come in to play is for flowering plants. Plants need both ends but easiest way to think about it, blue ends strong point is vegetative growth, red ends strong point is flowering in terrestrial plants. All plants need both ends to varying degrees but that is an easy way to think about it. In our tanks red waves don't travel as far and are used differently. Take some of the ludwigia species for example. In the emersed form several have flowers and look like weeds lol. Submersed form no flowers but we use the red waves to bring on varying shades of color on the same plant. Ludwigia senegalensis is a great example for this. Depending on how the spd between the bubs is manipulated you'll see brilliant yellows, oranges and reds. Glandulosa can get some really deep reds with adding in more red spectrum too.
Terrestrial par if I recall correctly is ~ 1600 in direct open sun while in shaded areas is ~ 90. In our tanks were trying to mimic the reduced light effect of a lake or river. Though, I did pull some beautiful red val from weeki watchi river several years ago which is spring fed and clear water for several miles lol. It had been nibbled on by a manatee and was floatiing so I scooped it up as I paddled haha.
Here are some citizen spd charts to give you a visual on the stronger reds in higher cri. Look at the 4000k line from about 630 over towards the 700's
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