I. "Visible Light Transmittance" and "Lens Density"
Visible Light Transmittance refers to the percentage of visible light that can pass through the lens. Conversely, Lens Density, also expressed as a percentage, indicates the darkness of the lens color, directly correlating to the percentage of visible light blocked. In the eyewear industry, these two metrics are commonly used in parallel; however, aside from the 50% value, they convey opposing meanings despite sharing the same percentage notation. For instance, a visible light transmittance of 60% corresponds to a lens density of 40%. While they represent the same concept from different perspectives, this can often cause confusion due to a lack of widespread understanding. We hope this clarification helps. The 60/40 lens we've developed is designed with a 60% visible light transmittance and a 40% lens density.
II. Functionality and Fashion
Photochromic lenses, which adjust their tint in response to UV or visible light exposure, are gaining attention as functional sunglass lenses. These lenses transition from a clear or lightly tinted state to a darker shade when exposed to sunlight. Although such lenses have existed since the 1960s, recent technological advancements have led to their rapid popularization. While photochromic lenses offer high convenience, they also present a fashion-related drawback: their color changeability. Maintaining a consistent, vibrant color regardless of UV or visible light exposure is often more desirable from a fashion perspective. Striking a balance between adequate sun protection during the day and a subtle tint suitable for indoor use, we arrived at a visible light transmittance of 60% and a lens density of 40%.
III. The Name "60/40 Lens"
Fashion enthusiasts may be familiar with the term "60/40 cross," referring to a classic American outdoor fabric composed of 60% cotton and 40% nylon. This durable, lightly water-repellent fabric retains the breathability inherent to cotton. While newer materials have surpassed its performance, the unique texture and appeal of this fabric remain timeless. Drawing inspiration from this enduring material, we named our lenses the "60/40 lens."