Utilization in the whirlpool

[Woolsocks]

Hi, I'm wondering if anyone has an estimated utilization rate for hops added to the whirlpool for aroma. I'm sure it varies with temperature and time. I typically circulate 85-90°C wort in the kettle for 15 minutes, rest it for 30 min, then draw off for 30-60 minutes, depending on how cold my tap water is that day.

And if anyone has a spectrophotometer they don't need.... I could just find out for myself!