CR-39 is a plastic lens available in an index of 1.50 or 1.56. Because this lens has a low index, it will be thicker for any given lens power. However, this is also the clearest type of plastic, producing the lowest wavelength aberrations of all eyeglass lens materials.
Polycarbonate is a plastic lens available in an index of 1.59. This lens has a moderate index and will not be as thick compared to CR39 for any given lens power, but also not as thin as other higher index lenses. Polycarbonate is super impact resistant and inherently UV blocking making it the lens of choice for safety eyewear, although it can scratch more easily than other types of plastic. Although polycarbonate has the highest amount of wavelength aberrations reducing it’s optical clarity, most wearers do not notice unless looking directly at lights or out of the sides of their glasses.
1.60 is a high-index plastic lens available in an index of 1.60. This is the first of the high-index lenses, creating thinner and lighter lenses than polycarbonate with better optical clarity. 1.60 high-index plastic is inherently UV blocking.
1.67 is a high-index plastic lens available in an index of 1.67. This is the second of the high-index lenses, creating thinner and lighter lenses than polycarbonate and 1.60 with better optical clarity than polycarbonate. 1.67 high-index plastic is inherently UV blocking.
1.74 is a high-index plastic lens available in an index of 1.74. This is the highest of the high-index lenses, creating the thinnest and lightest lenses available with better optical clarity than polycarbonate. 1.74 high-index plastic is inherently UV blocking.