VLT: 15. For medium to bright light. An all-purpose daytime lens with unbiased influence on color. Visible Light Transmittance (VLT) represents the percentage of light that passes through lens. For example, lens with VLT of 23 admits 23% of visible (non-UV) light, filtering out the remaining 77%. The lower the VLT, the darker the lens. Regardless of VLT, all ESS lenses provide 100% UVA/UVB protection.