Code 1640 (Dusky Blue) reflects 61.02% of incident D65 light. Measured in CAM16-UCS uniform space, Benjamin Moore Dusky Blue (1640) registers J'=84.5, a'=-8.78, and b'=-4.57 with HSL (188°, 21%, 79%) and Helmholtz-Kohlrausch perceived value 83.2 L*_HK. Because 1640 carries a*=-6.11 red-green and b*=-3.78 yellow-blue balance at chroma C*=7.18, Dusky Blue projects a cool cool coastal blue-grey character across drywall and millwork.
Thermal lighting shifts Benjamin Moore 1640 predictably. Under 5000K noon daylight, Dusky Blue (1640) holds its native #C5D0CB swatch; at 4000K cool office LED, 1640 adapts to #CCCEC2; at 3500K halogen, Dusky Blue transitions to #D1CDBD; at 3000K residential LED, 1640 warms to #D7CCB8; and under 2700K evening bulbs, Dusky Blue (1640) settles at #DCCAB4.
When cross-matching Benjamin Moore Dusky Blue (1640, #BDD1D4), Behr Cloudy Day (540E-2, #BCCED2, LRV 59%) scores ΔE2000=1.16 and CAM16=1.2, followed by Wind Speed (S450-2, ΔE=1.45). In Sherwin-Williams, Little Boy Blu (SW 9054, #C7D8DB, LRV 66.23%) achieves ΔE2000=2.12 ahead of Sleepy Blue (SW 6225, ΔE=2.18). Coordinate 1640 with Ice Mist (OC-67) ceilings, White (PM-2) trim, Icy Moon Drops (2056-70) hallways, and Snow White (2122-70) accents.