It is not a case of either/or with just cones operating during the day, and just rods being active in the eye at night. The human eye uses both rods and cones to see.
To accurately measure how the eye sees light, it must be measured on a different scale, where both rods and cones are in use, and such a Scale has been created.
The Scotopic/Photopic Ratio Scale, or
, is a multiplier that compensates for different types of light, and evaluates lumens of light very differently. The S/P Ratio determines how much light is “useful” to the human eye on a scale and provides a means of calculating
Visually Effective Lumens
(VEL’s) for a variety of light sources.