The alarm sounded and I opened my eyes and noticed that it was 5 am. Everything seems dark and I turned on the lights and my eyes instantaneously close as the bright light glare. It felt the same last night as I slipped into bed and the minute I turned off the light, I need to close my eyes before getting use to the dim surrounding.This phenomenal is due to the design of our eyes. Our eyes have two types of light-sensing cells called rods and cones.
The cones are responsible for bright light vision and the rods for night time vision. Cones have a peak response at about 555 nano-meters and rods have a peak response in about 505 nano-meters. Because both the rods and cones have different sensitivities, they are represented by two different sensitivity curves called photopic curves (representing the cone) and scotopic curves (representing the rod).
Photometry involves measurement of the psychophysical attributes of electromagnetic energy that is visible to the human eye. Photometry is the science of human perception.
Now imagine that you are driving into a tunnel. Bright and sunny highway into a dark tunnel. And your eyes sensors switches from photopic to scotopic. Your eyes shut tightly as you adjust to the dark condition for a second or two. And if you do continue your journey, leaving the dark tunnel into the bright highway ....
This is a major concern for highway engineers. The next time you drive into and out of a tunnel, notice the lighting into and leaving the tunnel, they are specially built to make sure you don't close your eyes. It is not about the lights only, there are instrumentation to make sure that lighting levels are balanced according to the time of the day (or night).
Happy cruising.
Photometry becomes a modern science in 1942, when Commission Internationale de l'Eclairage (CIE) metto define the response of the average human eye. CIE measured the light-adapted eyes of a sizeable sample group, and compile the data into the CIE Standard Luminosity Function (widely known as photopic curve -chromatic perception at normal state, and scotopic curve - achromatic perception at low level of illuminance.
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The retina is a highly specialized tissue lining the innermost portion of the eye. It contains millions of specialized photoreceptor cells called rods and cones that convert light rays into electrical signals that are transmitted to the brain through the optic nerve. Rods provide the ability to see in dim light while cones allow for sharp and color vision.
ReplyDeleteRead more about it: http://www.eye.com.ph/retina.htm