Below are the locations of the Signal Lenses in Horizon Forbidden West.
Lens of Dawn – Atop the Signal Tower in the northeastern part of the map, northeast of Chainscrape
Lens of Morning – Atop the Signal Tower northeast of Chainscrape at the Blocked Path
Lens of Midday – Atop the Signal Tower directly east of Chainscrape
Lens of Afternoon – Atop the Signal Tower near Twilight’s Landing, which is southwest of Chainscrape. You’ll come here during The Twilight Path side quest.
Lens of Twilight – Atop the Signal Tower east of Barren Light
Lens of Evening – Atop the Signal Tower north of Barren Light during the Signals of the Sun errand quest
After you obtain all of the Signal Lenses, travel to Barren Light and speak with Raynah near the Campfire to receive the Dune Shadow dye.