When you walk into an eyewear store to choose new lenses for your prescription glasses, it can be a bit overwhelming due to the multitude of lens materials available. Material is an extremely important factor as it significantly impacts your visual comfort, the aesthetics of your lenses, and your overall satisfaction. Among the many types of lenses available, high-index lenses and polycarbonate lenses are two very popular choices. What are the differences between these two lens materials? This guide will explore the characteristics, advantages, and potential drawbacks of high index lenses and polycarbonate lenses in detail to help you make an informed decision.
Overview of Hi Index vs. Polycarbonate Lenses
What Are High Index Lenses?
High index lenses are made from a plastic lens material with a high refractive index. Because they are made from a chemically synthesized compound, hi-index lenses can maintain thinness while providing enhanced visual acuity. The higher the refractive index, the thinner the lens can be for the same prescription strength. At their thinnest, high-index lenses can be up to 60% thinner than standard lenses, making them an ideal choice for those with higher prescriptions. The refractive index of high-index lenses typically ranges from 1.60 to 1.74.
What Are Polycarbonate Lenses?
Polycarbonate lenses, also known as poly lenses or PC lenses, are made from a durable, lightweight plastic material. They are widely used in both prescription and non-prescription eyewear and are renowned for their exceptional impact resistance. Polycarbonate was initially developed for aerospace applications and is now widely used in various optical products. It is especially popular in children’s glasses, safety glasses, and sports goggles such as swimming goggles. Polycarbonate lenses have a refractive index of approximately 1.59, making them thinner than standard plastic lenses but generally thicker than high-index lenses.
Hi Index vs. Polycarbonate Lenses: What’s the Difference?
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Prescription Strength
High index lenses come with refractive indices of 1.61, 1.67, and 1.74. Their thinner and lighter nature makes them suitable for higher prescriptions. Hi index lenses allow you to wear high-prescription lenses without the need for thick lenses that make you look like you have “bug eyes.” Polycarbonate lenses, on the other hand, have a refractive index of 1.59, making them suitable for low to moderate prescriptions. They offer a balance of thinness and durability.
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Weight and Thickness
At the same prescription strength, high index lenses are thinner than polycarbonate lenses. Generally, high-index lenses are the thinnest lenses on the market because most are aspheric lenses, with flat front and back surfaces. For myopia prescriptions, manufacturers can make the lenses flatter, thinning the lens center to as little as 1.5 mm. However, thinner lenses do not necessarily mean lighter lenses. Hi-index lenses are actually heavier than polycarbonate lenses, partly because high index lenses typically have a diameter of 75 mm for prescriptions below 8.00, whereas polycarbonate lenses generally have a diameter of 73 mm. If you need lightweight glasses for long-term wear and have a moderate prescription, polycarbonate lenses are a better choice as they are lighter and won’t put a burden on your nose.
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Impact Resistance
Polycarbonate lenses are highly impact-resistant, approximately 5 times more resistant than CR39 lenses, making them ideal for safety glasses, sports glasses, and children’s eyewear. While high-index lenses are also resistant to breaking and shattering, they do not offer the same level of impact resistance as polycarbonate lenses. This is why most children’s glasses and sports glasses use polycarbonate lenses.
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Optical Clarity
The Abbe value indicates the degree to which a lens disperses light. Lenses with lower Abbe values disperse light more, causing chromatic aberration, meaning different wavelengths of light focus at different points, leading to unwanted color distortion. High-index lenses have Abbe values ranging from about 33 to 41, while polycarbonate lenses have an Abbe value of around 32. Therefore, hi-index lenses provide better visual clarity and comfort with minimal distortion.
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UV Protection
High index lenses require an additional coating to provide UV protection, whereas polycarbonate lenses inherently offer 100% UV protection. At Aogang Optical, both high-index and polycarbonate lenses come with scratch-resistant and anti-reflective coatings, providing 100% UV protection.
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Cost
Compared to hi index lenses, which are more expensive, polycarbonate lenses are more economical, making them a better choice for those on a budget. Hi index lenses incur higher manufacturing costs due to the precision required in cutting and grinding to achieve their unique curvature. Polycarbonate lenses have much lower production costs but require specialized machines to prevent high-temperature debris from burning the lens surface during cutting.
Hi Index vs. Polycarbonate Lenses: The Choice Is Yours
Choosing between high index lenses and polycarbonate lenses ultimately depends on your specific needs. If you have a higher prescription, hi index lenses are a great option because they are thinner and allow for a wider selection of frames. If you prioritize lightness and durability, polycarbonate lenses might be the wiser choice.
By understanding the unique advantages and considerations of each material, you can make an informed decision that ensures optimal vision correction, comfort, and protection, tailored to your personal preferences. Whether you prioritize the thinness and clarity of high-index lenses or the durability and cost-effectiveness of polycarbonate lenses, both options offer reliable solutions to enhance your visual experience.
