Intrinsically photosensitive retinal ganglion cells measure light intensity linearly and adapt less well than cones.

“So the cones themselves have an incredible ability to adapt to different light conditions. So you can see at all different conditions. Otherwise it'd be a disaster. If you don't change the setting on your camera and you go from inside the room to the outside, it becomes completely white, you don't see anything. So if your cones don't adapt to the environment, then you're not going to be able to see in this room and on the beach, right? But the problem is your ipRCGs, the cells that we talked about, they measure intensity pretty well. They really know what intensity is. They have a very good linear measurement of intensity. They don't adapt as well. They don't adapt actually that much, to be honest.”