Psychology

The perception of light itself can be subjective. As Sir Isaac Newton told us, white light can be made to transform into various other colors of variable wavelength (Kusterer, 2007), some of which when mixed together result in other newer colors (Color Vision  Art). These colors, alongside transforming the world that we live in, tend to incite varying degrees of mood amongst humans and animals alike. While human perception of colors is somewhat subjective, some aspects of it can be said to have universal implications. The color red and others close to it such as orange and yellow are considered to be warm colors that incite feelings ranging from comfort and warmth to that of anger and hostility. Colors surrounding the blue end of the spectrum such as purple and green are observed to incite feelings of calmness, but may even resort to sadness or indifference depending upon the perceivers inclinations. These ideologies are what the ancient civilizations purported to use in their Chromotherapy sessions, using colors to heal and effect a persons mood in a positive way (Wagner) (Parker, 2001). Although some of the aforementioned ideologies may be generally accepted if perhaps still prone to skepticism at the hands of leading psychologists, it brings us to consider what exactly our eyes and its complementing visual system is designed to perceive, and its limitations. The anatomical details involved in the process include the photoreceptor mosaic on the retina, its sensitivity and properties of the object emitting the light.

The source could either be direct, such as from a light bulb, or reflected off of objects. The eye is designed to perceive that light where as the brain does the part of determining its origins and contrast it with an image. The multipurpose nature of the eye renders it in charge of refracting light through the cornea, control the amount of light entering the eye through the pupil, focus it to cast a picture on the retina and direct it via the optical nerve as electrical signals to the brain. Together this makes up the perception system of an individual, which has its own way of dealing with the varying degrees of light. The object of this paper is to discuss the changes the eye undergoes as dependent upon the light it perceives.

Light perception depends partly on the sensitivity properties of the photoreceptor mosaic on the retina. The mosaic comprises of three cone-type (responsible for perceptions of color) cells and one rod-type cell which alter themselves depending on the prevailing light conditions. The rod type cells are responsible for allowing low light visibility, and take over gradually as the light drops. The photoreceptor cones are active in brightly lit areas, sharing their contribution with the rods as the light gradually gets dimmer, so that at night when the light intensity is at its lowest (such as in moonlight), the entire vision is managed by rods.

Cones and rods have their own distinct characteristics when it comes to dealing with light. Where cones permit the perception of color, they also allow the retina to capture more detail than the rods would allow. Their response time is swifter than rods and as a result, their reaction to changing images is faster as well (Kandel, Schwartz,  Jessell, 2000). The transition from cone mediated vision to rod mediated vision is a particularly interesting phenomenon, and can be observed very easily by holding a torch in the dark and pointing it straight into the eye in front of a mirror. The pupil shrinks instantly, and the uncomfortable source of light (from the torch) is immediately detected. Contrast this reaction to when the torch goes off immediately afterwards, a faint bright spot is still visible after the source of light has stopped as the rods take over and try to adjust to the lack of light sources. This is a good example of the difference in response times between the two photoreceptors and the constraints placed upon the system by the front end.

Practical Assessment Exercise
The aforementioned transition from one extreme (cone receptors only) to the other end of the spectrum (rod only) can be more practically observed and felt from the first person perspective by observing a gradual change in lighting conditions. The torch example was too immediate and does not cover gradual, prominent changes in light intensity. Observing the sunset or sunrise would provide a good alternative for observing such a change, and thus I chose the latter for the purpose of this exercise.

The best position to take in order to observe the light changes especially in an urban setting is near the beach. The view of the horizon means the rising sun would be in clear view. Prior to the advent of dawn, and under the moonlight, the rod photoreceptors are at work and looking around the citys night lights does not yield much of a change whereas turning back to the skyline puts the black skyline into perspective. There is an obvious lack of perceptive colors, except for the grey of the clouds and the black of the sky, a feature dealt with by the cone receptors. As dawn begins to emerge, the movement of the clouds becomes more prominent. Light starts seeping through the horizon lighting up the sky in a distinct but slow fashion. Observing the intensity of light gain momentum this gradually makes the world transform right in front of your eyes. At this point it is hard simply to concentrate on the changes to the environment as it is a thought provoking setup, causing the mind to wander.

As dawn transitions into sunrise and light engulfs the sky, right before the tip of the sun is visible the world delves into rich perceptive colors that are easily distinguishable from the light orange of the dawn. As the sun rises, its initial brilliant shades of orange and yellow immediately strike the eye, transforming the world into a brighter place. The sun, previously bearable, now starts to gain intensity as it rises, filling up the horizon with startling shades of yellow until its visible fully, but quickly becoming hard to bear. Once the sun gains full intensity, the world becomes detailed, with smaller distant objects becoming part of the picture. Color variations are more prominent now throughout.

Reflection
The transition from rod-only vision to cone only vision was of particular interest during the transitory phase. In the beginning, as dawn starts to loom, the rod-only light-sensitive mosaic tends to retain whatever light its receiving from the moonlit beachfront, making way for the cone receptors to take over as dawn is in full swing. From this point on, the response to colors and the light changes are much sharper and faster, suggestive of the characteristics of cones. The vivid display of colors throughout the sky as the sun rears its head from the horizon also indicates that the cones are actively receiving long, medium and small wavelengths with the rising intensity of light. By the time the sun reaches its full glory, the eye lids shut themselves half way, indicative of the fact that although we are in cone-only mode, there is still light seeping in than the human retina can bear.