What does darkness do

How Eyes See at Night. How do we see in the dark? Our vision range in varying light conditions comes from three parts of the eye: The Pupil: The eye in many ways is like a camera. The pupil works in a similar fashion. It will get very small in bright light to physically block the amount of light reaching the retina and will open wide in the darkness.

Rod and Cone Cells: Our eyes use two different types of cells to see light: rods and cones. The cone cells perceive fine detail and color but need bright light in order to do so.

Rod cells can only see black and white and have poor resolution, but remain sensitive even in very low light. A white barely seen by the rods must be increased in brightness 1, times before the cones can pick it up.

Photopigments: Both rods and cones contain light-sensitive chemicals called photopigments. You can see in the dark, or at least in very low light. If you flip off the lights, your pupil will immediately open up. Your photorecepters start to improve their sensitivity, to soak up whatever light they can in the new dim conditions. The cones do this quickly — after about five minutes, their sensitivity maxes out.

After about 10 minutes in a darker place, your rods finally catch up and take over. Try it. Find a very dark place, maybe your bedroom at night. Turn on whatever light you have and gather some colorful objects. Spend some time noticing how colorful, sharp and full of contrast things look.

Then turn off the lights and watch how the appearance of your room and objects changes over time. First it will seem very dark; then you will rapidly see better, thanks to your pupils and cones doing their jobs. We slept in a different way than we do now. The dark lasted about twelve hours and during this time people slept for eight or nine hours in two separate bouts, and were awake, but in the dark, for another three or four hours. Everything changed when electric lighting was invented in the latter part of the 19th century.

Since then there has been an ever increasing assault on dark. Outdoor environments are relentlessly lit, and more and more people use computer tablets and smart phones at all hours, bathing their faces in bright blue light at times of day when they should be transitioning to nighttime physiology.

When people get away from the city and its artificial light to go camping, they often notice a marked improvement in their sleep. A recent study has verified this effect. Today, most of us get too little light during the day and too much at night for our circadian rhythm to function at its best. It is the rare person who sleeps in a completely dark bedroom, and many people get very little sunlight because they work inside all day long. What can you do for your circadian health?

Get bright, blue light in the morning preferably from the Sun , and use dim, longer wavelength light more yellow and red like incandescent in the evening. And sleep in the dark.

Portsmouth Climate Festival — Portsmouth, Portsmouth. The same is true of galaxies in clusters, which leads scientists to believe that something we cannot see is at work. They think something we have yet to detect directly is giving these galaxies extra mass, generating the extra gravity they need to stay intact. Unlike normal matter, dark matter does not interact with the electromagnetic force.

This means it does not absorb, reflect or emit light, making it extremely hard to spot. In fact, researchers have been able to infer the existence of dark matter only from the gravitational effect it seems to have on visible matter.