D means that the product is rated in its category in terms of energy efficiency. The Energy Labeling system is based on EU Regulation 2017/1369/EU. D ASUS VP229HE, 54.6 cm (21.5"), 1920 x 1080 pixels, Full HD, LED, 5 ms, Black ASUS VP229HE. Display diagonal: 54.6 cm (21.5"), Display resolution: 1920 x 1080 pixels, HD type: Full HD, Display technology: LED, Response time: 5 ms, Native aspect ratio: 16:9, Viewing angle, horizontal: 178°, Viewing angle, vertical: 178°. VESA mounting. Product colour: Black