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What do you think of 80% Lower Half Facet Length?

In general, from what I have noticed, a steep/shallow combo, say 35/40.6 or even 36/40.6, tends to produce more contrasty appearance than say 35/40.8 or 35/41. Such combo often has lower LGH in general. As a result, the combination of the two can make the arrows look defined, bigger and pop.

Having that said, nothing wrong with the diamond you posted in regards to LGH and arrows. The arrows don't appear well defined probably because of photography issues (tilted diamond, out of focus)

75% is not necessarily more preferable than 80%, as 75%=73~77%, and 80%=78%~82%, according to GIA's rouding.

You don't want your diamond to be too contrasty either, like this.
https://www.jamesallen.com/loose-di...k-color-vvs2-clarity-excellent-cut-sku-614165
 
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I don't think the arrows are less defined but they are skinnier. It might not make any difference to you though - hope you love the stone! Be sure and take pictures for us when it arrives!
 
Although I do prefer fatter arrows, I don't think these are TOO skinny. GIA rounds their numbers so this is probably more like 78/79 rounded up. The flashes of light will be more of a pinpoint sparkle versus bolder flashes from lowers closer to 75. For example, I would consider these TOO skinny...probably 81/82 lower halves: https://www.jamesallen.com/loose-di...i-color-si1-clarity-excellent-cut-sku-2672843
 
Thanks so much, appreciate your feedback!
 
In addition to what's mentioned, longer LGF tend to perform better in an abundance of light, fatter arrows with shorter LGF tend to perform better in light starved environments. I believe Rhino I think it was had/has a soft spot for longer LGF and you can get bold flashes with skinny arrows from the half pavilion mains in a well cut diamond.

GOG has nice educational videos on LGF on YouTube.
 


1st video is educational, second video demonstrates differences well. Generally in these videos longer LGF look better because of the strong lighting
 
My wife's stone is 80% LGF and it looks good to me, but if you prefer fatter arrows then go with a 77% LGF.IMG_2965.JPG
 
Thanks very much everyone! The information is helpful!
 
Do note that GIA doesn't report the actual Lower Half length average. They round it to the nearest 5%. So you will only see 75% or 80% printed on the report.

For this diamond I estimate that facet group's actual average at high 77 or 78% (I modeled this wireframe at 78%).

170419-lower-halves.jpg
 
Wow John, thank you so much. That is absolutely amazing information!
 
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