Back glare on glasses occurs when light hits the back surface of your lenses and reflects directly into your eye. This reflection, often caused by overhead lighting, windows, or light sources positioned behind you, reduces visual clarity. It can cause eye strain, discomfort, and visual distortions, making tasks like driving or working on a computer screen difficult. Finding solutions to this reflection improves your overall visual experience.
The Essential Solution: Anti-Reflective Coatings
The most effective method for eliminating back glare involves applying an Anti-Reflective (AR) coating to the lens surface. An AR coating is a microscopically thin, multilayered film typically made of metal oxides that are applied to both the front and back of the lens. This coating works by using destructive interference, disrupting the light waves that reflect off the lens.
When light passes through an uncoated lens, approximately 8% of it reflects off the surfaces. The AR coating is engineered to have an index of refraction between air and the lens material, causing two reflected light waves from the film to cancel each other out. This cancellation minimizes the reflection, allowing up to 99.5% of available light to pass through the lens to your eye.
While a full AR coating is applied to both sides for maximum benefit, the application to the back surface specifically addresses back glare. This inner coating stops light coming from behind the wearer from bouncing off the lens and into the eye. High-quality coatings often involve multiple layers, alternating between high and low refractive indexes, which increases their effectiveness across different light wavelengths.
Some modern AR coatings also incorporate a hydrophobic surface treatment, which helps repel water and makes the lenses easier to keep clean. A clean lens surface will have fewer imperfections to scatter light and create additional reflections. Although the coating eliminates reflections, the chemical compounds used may sometimes cause a slight residual tint, often green or blue, when light hits the surface at an angle.
Immediate Adjustments for Glare Reduction
While coatings offer a long-term fix, immediate relief from back glare can be found through simple adjustments to your environment and posture. The goal is to prevent light sources from hitting the back of your lenses at an angle that directs the reflection into your eyes.
When using a computer screen, try lowering the brightness setting to match the ambient light in the room. You should also position any overhead or desk lamps so they are not directly behind you, as this is the most common cause of the reflection. If possible, elevate the light source so it is above your head and slightly to the side, directing the light away from the reflective angle of your glasses.
Minor physical adjustments can also temporarily mitigate the issue when changing the light source is not an option. Slightly tilting your head or adjusting the angle of your glasses can change the angle of incidence. This small shift can redirect the reflected light away from your eye. Additionally, ensuring the environment behind your head is not significantly brighter than the environment in front of you reduces the amount of light available to cause back glare.
How Frame and Lens Choices Influence Glare
The physical characteristics of your glasses, including the frame style and lens shape, play a significant role in how much back glare you experience. The curvature of the lens is a contributing factor, as highly curved or wraparound styles can catch more peripheral light. Lenses with a flatter base curve generally reduce the area available for light to enter from the periphery and reflect inward.
The fit of the frame on your face is also a major influence on back glare. A proper fit ensures the lenses sit close to your eyes, minimizing the gap through which stray light can enter. If a frame is too large or sits too far away from your face, it increases the opportunity for light to strike the inner surface of the lens and reflect directly into your vision.
The material and design of the lens itself also affect reflection before any coating is applied. High-index lens materials, which allow for thinner and lighter lenses, tend to reflect more light than standard plastic lenses. Regular plastic lenses reflect around 8% of incoming light, but high-index lenses can reflect up to 50% more, making an AR coating necessary. Choosing a smaller frame size may also help minimize the reflective surface area, especially for individuals with higher prescriptions.