Light’s Measure /Colored Perceptions

Light is a form of electromagnetic energy. Our eyes are sensitive to a narrow slice of the electromagnetic spectrum,8 and color is our response to being stimulated by energy at those wavelengths. If color can be said to exist outside our heads, it is a property of light. The light thatês transmitted through or reflected from the objects in our world is part of color that we can measure.


We can describe light in terms of its wavelength; the unit we use is called a nanometer (NM), which is one millionth of a meter. Visible light is that part of the electromagnetic spectrum whose wavelengths range from 380 nm to about 750 nm. Immediately below this range lies ultraviolet radiation, while immediately above it lies infrared radiation, or heat. But light does not exist as a single wavelength. Isaac Newton showed us that when a beam of sunlight is passed through a prism, the white light is dispersed into a spectrum: white light, therefore, is made up of all the visible wavelengths. The behavior of prisms was well known before Newton’s time, but it had been assumed that the prism somehow added color to the light; Newton’s discovery was that colors were actually present in white light all along. If we look a little closer, we find that white light is itself something of an abstraction. The light from the northern sky (sometimes called painter’s light) is quite a bit bluer than direct sunlight, which is in turn bluer than the light from an incandescent light bulb. These light sources differ in relative intensities.


While we can measure quite precisely the stimuli that causes us to perceive light our response to those wavelengths is affected by a whole host of factors. Physiology, psychology, culture, and even the language we speak all influence our perception of light in subtle ways that resist quantification.


How Light Interacts with Objects

Even though light seems to have a certain color, the light itself isn’t colored. Rather, itês the way the light interacts with objects that causes the stimulus that provokes our sensation of color. When light strikes an object, one or more of these things can happen: the light can be transmitted through the object, absorbed by it, or reflected by it.


When the light is transmitted through the object, we say that the object is transparent. In a colorless object ie. a pond or river,all the light is transmitted except for a small amount that is reflected on its surface. that is why we can see transparent objects like glass or water-if all the light were transmitted they would be invisible. When you put one end of a tree branch into water, it appears to bend: but it isn’t the branch that is bending, just the light that allows us to see the branch. This phenomena is called refractive indexing. Refractive index is itself something of an abstraction. It is really a measure of how much light slows down as it passes through the material.


Light can also be absorbed by an object. If the material absorbs part of the light and transmits the rest, it appears colored but still transparent. If all the light is absorbed , the material appears black and opaque.


Lastly, light can be reflected by the object. A glossy surface will produce specular reflection, where the incoming and outgoing beams of light are at equal angles relative to the surface. Mirrors are speculative reflectors. But most surfaces are irregular and hence scatter light in many different directions. Scattered light is termed diffuse reflection. If some light is scattered and some are transmitted , the object appears translucent; if all the light that strikes an object is either scattered or absorbed, the object appears opaque.


When perceiving light of any kind whether refractive or specular our minds actually interpret the signals our eyes generate in terms of these attributes both scientifically and aesthetically.

© Copyright 1997 Denise Urban