Understanding Photochromic Lenses: Principles, Types, and Their Pros & Cons

When selecting photochromic lenses, understanding the underlying principles, different types, and their respective pros and cons is essential for making an informed decision. Whether you need lenses that quickly adapt to changing light conditions or ones that maintain consistent tint across varying prescriptions, this guide offers a comprehensive overview. Learn how base photochromic lenses and coated photochromic lenses differ, and discover which type best suits your vision needs, lifestyle, and environmental demands.

Principle of Photochromic Lenses

Photochromic lenses react to ultraviolet (UV) light, thanks to microcrystals of silver halide and copper oxide embedded within. Under strong light, these microcrystals darken the lens, and when the light diminishes, the lens returns to its lighter state.

The following is a brief summary of the principles and categories of photochromic lenses, and the advantages and disadvantages of the two categories:

Base Material Photochromic Lenses

How It Works: Photochromic refers to the discoloration in the lens substrate (which can be understood as the lens material itself). Substrate photochromic refers to the chemical reaction of silver halide and copper oxide added to the substrate under light.

Advantages:

• Cost-effective.
• Wide range of colors.
• High heat resistance.

Disadvantages:

• Slower color change.
• Uneven color distribution, especially noticeable in high-prescription lenses where the lens thickness varies.
• Slight color variation between the center and edges of high-prescription lenses.
• There are fewer color-changing product lines, mainly focusing on 1.56 and 1.60 refractive index.

Coated Photochromic Lenses :

How It Works: These lenses feature a special coating that changes color based on UV light exposure. The coating is applied to the surface, ensuring uniform color change across the lens.

Advantages:

• Rapid color change.
• Enhanced stability and consistency in color change.
• Compared with Base Material Photochromic Lenses, it changes color more evenly.
• There are no restrictions on lens power, material, thickness, etc., and the lenses fade quickly and evenly; progressive lenses, blue light protection lenses, etc. can also be made.

Disadvantages:

• Higher cost compared to base material lenses.
• The discoloration time is short, the discoloration is easy to occur at high temperature, and the film layer is easy to be scratched.

Considerations and Recommendations

When choosing photochromic lenses, the decision between base material and coated lenses often comes down to personal preference and specific needs:

Base Material Lenses: Suitable for those seeking a cost-effective solution with high heat resistance and a broad range of colors, albeit with a slower color change and potential for color variation.

Coated Lenses: Ideal for users who prioritize rapid and consistent color change, regardless of lens prescription, and are willing to invest in higher-cost lenses.

For consumers with low to moderate prescriptions who prioritize fast color-changing efficiency, base photochromic lenses are recommended.

For those with higher prescriptions or specific functional requirements, such as blue light blocking, progressive polarization, or high refractive indices like 1.67 or 1.71, coated photochromic lenses are a better choice.

Both types of lenses have advanced significantly, and current technology has minimized the differences in performance. Thus, selecting the right lens often depends on your specific visual and aesthetic requirements.