Scotopic vision operates below roughly 0.005 cd/m squared, where only the rods respond. It has no color discrimination, poor acuity and no response in the fovea, and its sensitivity peaks at 507 nm, so bluish light looks relatively brighter. The ratio of a source's scotopic to photopic output, the S/P ratio, is quoted for outdoor sources whose users see in low light.
Out on that trail you're nearly scotopic, so the cooler source will actually look brighter even though the lumens are the same.
Also heard as
- scotopic vision
- rod vision
- night vision
Related terms
Photopic
Describes daylight vision, when cones dominate, providing color and sharp detail at luminances above a few cd/m squared.
Mesopic
Describes the in-between vision of twilight and street lighting, when rods and cones both contribute.
V-lambda curve
The standard curve of the eye's daytime sensitivity to each wavelength, peaking in green at 555 nm.
ipRGC
Intrinsically photosensitive retinal ganglion cells: eye cells that sense light for the body clock rather than for vision.