Are There Any Advantages to “Low Index” Lenses over High Index?
When most of us think about high index lenses, we automatically assume that they’re better than the “standard” or “low index” lenses at the eye doctor’s office.
Advantages of Low Index over High Index Lenses
These standard lenses, though, are sold to a large portion of eyeglasses wearers worldwide, and they’re worn in all sorts of special applications. This begs the question, then, “Are there any advantages to low index lenses, other than their affordability?” The answer is yes, but only in certain circumstances. Here are the times when standard or low-index lenses are a better choice than high index plastic:
- If you do not have a strong prescription (combined sphere and cylinder power above +2.50 or below -4.00), the difference between high index plastic and a standard plastic or polycarbonate will be barely or not at all noticeable. In other words, there’s little point in spending the extra money.
- Polycarbonate is more impact-resistant than high index plastic, so it is better in safety or sports situations when you need to protect your eyes.
- If you want special lens colors, such as polarized and transitions, you will be more likely to find the lens in a standard material than in high index plastic.
- If you want a larger lens size in a wraparound frame, you will have a hard time getting it filled in high index plastic because the lenses are rarely made in large enough diameters. Most wraparound and sports frames have lenses that curve and are pretty big, and it’s hard or impossible to accommodate that with the lens diameters typical of high index plastic.
- In general, high index lenses have a lower Abbe number and higher color aberration (color blurring and distortion), which can have an effect on their clarity. They also are highly reflective, requiring anti-reflective coating on the high index lens to get rid of glare. Standard plastic and polycarbonate lenses do not have these problems.
Lens clarity, safety, customization options… all of these are reasons to reconsider high index plastic. The bottom line, however, is that if you have a strong prescription, high index plastic is probably going to improve your comfort and the look of your everyday glasses. It is an excellent choice for your main pair of glasses if you have a strong prescription. If you are getting a second pair for safety, or in a wraparound pair of sunglasses (and your prescription isn’t too high for a wraparound frame), you should consider getting polycarbonate or standard plastic. High index plastic is a great lens material, but hopefully now you know when not to use it. Thanks for reading!