Glowing Things

[Shadow_Demon]

I was wondering (again) how and why things seem brighter when you aren't looking directly at them, yet not with things like a fluorescent bulb, tube or the sun.

EG: A glow in the dark object, like the small stars (less then 5mm in diameter) on my ceiling in my room.

[gen2]

You have two types of receptor on the retina of your eyes. They are called rods and cones. Cones are only sensitive to one third of the visual spectrum (either red, green or blue light). Cones are found mostly in the centre of the field of vision.

Rods are sensitive to any frequency of visual light. ie they are three times more sensitive than the cones (but cannot distinguish between different colours). Rods predominate around the peripheral visual area.

Therefore, in dim light, faint objects are seen three times more brightly by your peripheral vision than by your central vision.

[theprof]

Another good answer from gen2.

If I could just add that you can demonstrate the sensitivity of rods and cones by the old trick of very slowly bringing an upright pencil from around the ear on one side of your head into your full field of vision in front of your eyes.

Stare straight ahead and keep the pencil a couple of inches away from your head as you're doing it. You'll reach a point where the pencil is visible in your peripheral vision but you'll be unable to tell it's colour ie it's in monochrome.

This occurs because the rods have detected the pencil but the cones in the centre of the field of vision, are not able to see it yet. This causes the brain to perceive the pencil as being in monochrome. When the pencil is brought into the field of vision of the cones, it is then seen in full glorious colour.

[chakka35]

Two brilliant answers. Well done, gen2 and theprof. Thank heavens someone knows what the primary colours are.