Two forces are simultaneously pushing outdoor lighting towards warmer color temperatures: ecology, and human comfort.

The ecological rationale has to do with the blue part of the spectrum. Shortwave light scatters more strongly in the atmosphere and affects insects, birds and nocturnal animals more significantly. Many city and provincial lighting regulations currently specify maximum correlated color temperatures for newly installed luminaires, with common upper limits of 3000K or lower for residential streets, parks and ecologically sensitive areas. Even if the specific values vary from place to place, the direction is clear.

The reason for the comfort level is related to glare. Outdoor lighting is ultimately evaluated by the human eye. The same luminous flux, projected by a warm color light source with a good shading angle, will be softer and easier to recognize than a cool color light source directed horizontally.

In practice, this means that lamp selection has shifted from "just looking at light output" to "looking at light distribution control". Optics design for shading, the upper light ratio (ULOR), which leaves light on the road instead of shooting into the sky, and warm color temperatures are increasingly being written directly into specifications rather than leaving it to suppliers to decide.

The safe default value for residential projects is 3000K; for parks and historical districts, 2700K is often more suitable; and main roads are places where 4000K can still stand-and it's best to explain why.