When light encounters an object, it engages in various interactions that shape how we perceive the world. Light is a form of energy, electromagnetic radiation, traveling in tiny packets called photons. The portion of this radiation detectable by the human eye is visible light, encompassing wavelengths roughly between 380 and 750 nanometers. These interactions are fundamental to our visual experience, influencing the colors we see and the clarity of objects around us.
Light’s Fundamental Interactions: Reflection, Absorption, and Transmission
When light strikes a surface, one of several primary interactions can occur: reflection, absorption, or transmission. Reflection happens when light bounces off a surface, changing its direction. This can occur in two main ways: specular reflection, where light reflects uniformly from smooth, shiny surfaces like a mirror or calm water, allowing for clear images; and diffuse reflection, where light scatters in many directions from rough or uneven surfaces, which is why we can see most everyday objects.
Absorption is the process where an object takes in light energy, converting it into another form, most commonly heat. When light is absorbed, it no longer remains visible, explaining why dark surfaces become warm in sunlight. The atoms within a material capture the photon’s energy, transforming it into internal energy.
Transmission describes light passing through an object. Transparent materials, such as clear glass or clean water, allow light to pass through with minimal scattering, enabling clear vision. In contrast, translucent materials, like frosted glass or wax paper, also allow light to pass through but scatter it, resulting in a blurred view of objects on the other side.
How Light Creates Color
The color an object appears to have is not an inherent property, but a result of how it interacts with illuminating light. Visible light is comprised of a spectrum of colors, often remembered by the acronym ROYGBIV, each corresponding to different wavelengths. When white light shines on an opaque object, its atomic structure selectively absorbs certain wavelengths and reflects others.
The wavelengths reflected are what our eyes perceive as the object’s color. For instance, a red apple appears red because it absorbs most wavelengths but reflects primarily red light. A green leaf absorbs blue and red wavelengths while reflecting green light. Objects that appear black absorb nearly all visible light, reflecting almost nothing. Conversely, white objects reflect almost all visible light, appearing white.
Light Bending and Spreading: Refraction and Scattering
Beyond reflection, absorption, and transmission, light can also undergo phenomena involving changes in direction. Refraction is the bending of light as it passes from one medium into another, such as from air to water or glass. This bending occurs because light changes speed as it moves between materials with different optical densities. A common observation of refraction is a straight straw appearing bent when partially submerged in a glass of water. Lenses in eyeglasses or cameras utilize refraction to focus light and form images.
Scattering is a process where light is redirected in multiple directions by particles within a medium. Unlike reflection, which typically involves a surface, scattering occurs when light encounters particles comparable to its wavelength or larger. This phenomenon explains why the sky appears blue; tiny gas molecules in the atmosphere scatter blue light more effectively than other colors. Fog or clouds appear white because their larger water droplets scatter all visible light equally, distributing it in many directions.