#5 is way too dark for brazing. I used to use a B3 series glassblowing lens from Wale Apparatus
https://www.waleapparatus.com/category/wale-wear when I was fillet brazing. They are a bit pricey, but it makes it easier to see the difference between molten flux and molten brass.
I switched to TIG welding, but I still braze in bridges and braze ons. I usually just use a pair of dark sunglasses for those tasks.