Transparent or Translucent Materials
Not all materials are opaque to sunlight. Transparent substances such as glass, plastic, and water transmit light directly, while materials like tracing paper, clouds, and ground glass diffuse the light they convey, classifying them as translucent.
When these materials are colored, they selectively transmit wavelengths of light corresponding to their color. For instance, deep red glass will transmit red wavelengths but can be nearly opaque to blue light.
Translucent materials, by diffusing light, create a milky appearance when illuminated and produce a more uniformly lit environment compared to transparent materials, even if the light source is not directly behind them. Slide previews and light boxes operate on this principle, providing a quality of light similar to that reflected by a white diffuse surface.
Refraction
When direct light travels obliquely from the air into another transparent medium, interesting effects occur. As light enters a denser medium, such as glass, it slows down and changes direction due to refraction. This is analogous to driving a car at an angle into sand, where one part of the car slows down first, causing a shift in direction. This phenomenon is crucial in lens design, as lenses utilize refraction to bend light and form images.
Refraction can be observed when a stick is pushed straight into clear water, appearing bent at the water’s surface. Similarly, thick windows may produce distortions. Refraction only affects light entering obliquely; light hitting the boundary perpendicularly slows down without changing direction, while light striking at a very shallow angle is mostly reflected.
The Complete Picture
Everything we perceive in our environment is a result of the interplay of light effects: diffuse and specular reflection, absorption, transmission, and refraction. For example, an apple illuminated laterally by direct sunlight reflects the colored wavelengths of its lit half. Most of this reflection is diffuse, but the apple’s smooth skin also produces a specular highlight where the sun’s angle aligns with the angle to the observer’s eye.
The shape and shadow on the apple further inform its three-dimensional form. Our eyes and brain interpret these subtle light cues to understand the object’s strength and roundness without physical contact. This ability to “see” is what photography captures, making the image permanent and shareable. However, film and digital sensors cannot perfectly replicate human vision, as different films record light and color uniquely. With experience, photographers learn how their chosen medium reacts to light and shadow. High-specification digital cameras allow for color adjustments, but they still cannot fully replicate the human eye’s perception, adding to the magic of photography by transforming our visual reality into a tangible image.
