The experience of seeing subtle color fringes or faint halos around bright objects, often described as “rainbows” in your glasses, is a common optical phenomenon. These colored edges are usually most noticeable when looking at high-contrast scenes, such as streetlights at night or dark text on a bright screen. The presence of these color effects is generally harmless and is a predictable consequence of how light interacts with lens materials. Recognizing this visual artifact as chromatic aberration is the first step toward understanding its cause and minimizing its effect.
Understanding Light Dispersion
The fundamental reason you see these rainbow effects lies in a physics principle known as dispersion, which results in chromatic aberration. White light is a composite of all the colors of the visible spectrum, each corresponding to a different wavelength. When this light passes through a transparent medium, such as a corrective lens, the speed of each color changes slightly, causing the colors to bend, or refract, at slightly different angles. Shorter wavelengths, like blue and violet, bend more sharply, while longer wavelengths, such as red, bend less. The failure of the lens to focus all these colors to the exact same point creates the color fringing you perceive.
The Role of Lens Materials and Design
The degree to which a lens material disperses light is quantified by the Abbe value. Materials with a higher Abbe value disperse light less, resulting in less noticeable color fringing. Conversely, materials with a lower Abbe value have greater light dispersion and are more prone to chromatic aberration.
Many modern lenses, particularly those made from high-index plastics, are designed to be thinner and lighter to improve aesthetics and comfort. While beneficial for thickness, these high-index materials often have a lower Abbe value, which increases the potential for the rainbow effect. For example, standard plastic (CR-39) has a relatively high Abbe value around 58, while some high-index or impact-resistant materials like polycarbonate can have values as low as 30, making the color fringes more apparent. This effect is also exacerbated by strong prescriptions because higher lens power induces more light deviation, pushing the chromatic aberration further out into the peripheral vision.
Poor manufacturing, such as lenses that are not perfectly centered or surfaced, can also contribute to the issue by introducing unintended prismatic effects. Even if the lens material has a good Abbe value, any optical misalignment will increase the degree of light deviation and the resulting color separation. The combination of a low-Abbe value material and a strong prescription is typically what makes this phenomenon most noticeable for the wearer.
Practical Ways to Minimize Rainbow Effects
The application of an Anti-Reflective (AR) coating is one of the most effective ways to mitigate the visual annoyance of color fringing. These specialized coatings reduce internal reflections within the lens, which can amplify the appearance of the rainbow effects. While AR coatings do not eliminate chromatic aberration itself, they significantly improve visual comfort by allowing more light to pass directly through the lens.
When selecting new eyewear, discuss lens material alternatives with an eye care professional. If thickness is not a major concern, opting for a material with a higher Abbe value, such as standard plastic or crown glass, will inherently reduce light dispersion. This material choice directly addresses the underlying cause of the aberration.
If the rainbow effects appear suddenly or become significantly worse, it is important to consult your optometrist to check the fit and accuracy of your prescription. A simple adjustment to the frame or a minor change in lens power can correct an unintended prism effect contributing to the visual disturbance. Ensuring the lenses are correctly centered and aligned with the visual axis helps minimize lateral chromatic aberration.