Photochromic lenses(transition lenses), are eyeglass lenses that can automatically adjust their color based on changes in the surrounding light conditions. Generally, outdoor photochromic lenses take about 30 seconds to darken to 80%. In the presence of intense sunlight, this darkening time is even shorter. Moreover, within the first three minutes of exposure to outdoor light, the tint on the lenses continues to deepen until reaching its darkest shade. Upon returning indoors, the lenses can revert to 10% transparency within three minutes or even faster.

The specific time required for photochromic lenses to adjust their tint can vary depending on factors such as temperature, UV intensity, the age of the lenses, and the brand.

How Photochromic Lenses Work?

The surface of photochromic lenses is embedded or bonded with silver halide or organic photochromic materials. These molecules undergo a chemical reaction when exposed to ultraviolet (UV) light. Each photochromic lens contains trillions of sunlight-sensitive molecules that change shape and structure upon UV exposure, absorbing visible light and causing the lenses to darken.

Since these lenses react to UV light rather than visible light, they automatically darken outdoors—even on cloudy days—but remain clear under artificial lighting. Conversely, when the lenses return to a low-UV environment (such as indoors), the molecules revert to their original state, causing the lenses to lighten or become transparent again.

The transition process (darkening or lightening) is also influenced by temperature. In cold weather, the molecules inside the lenses move and transform more slowly, requiring more time to darken. In hot weather, the lenses may adjust their tint more quickly.

Additionally, photochromic lenses absorb 100% of UVA and UVB rays, providing full protection against the sun’s most harmful radiation. Like sunglasses, they help reduce the risk of eye conditions caused by prolonged sun exposure, including cataracts, macular degeneration, corneal sunburn, and retinal tissue damage.

How Quickly Do Photochromic Lenses Work?

Generally, modern photochromic lenses begin to darken within 15 to 30 seconds after being exposed to sunlight, and most lenses reach their darkest state within 60 to 120 seconds. Compared to darkening, it usually takes longer for the lenses to return to clear. After leaving a UV environment, they typically begin to lighten within 1 minute, but it may take 2 to 5 minutes to fully return to a transparent state. However, Aogang now offers a new type of photochromic lens that darkens in an even shorter time and reaches a deeper shade than standard photochromic lenses.

Factors Affecting the Transition Speed of Photochromic Lenses

Several factors influence the transition speed of photochromic lenses, including:

• Temperature

The reaction speed of photochromic lenses is affected by temperature. Typically, lower temperatures slow down the darkening process and the reversion to transparency, as molecular movement slows in cold environments. Conversely, in warmer temperatures, lenses adjust their tint more rapidly.

• UV Intensity

The speed at which photochromic lenses transition is directly related to the intensity of UV light. In strong UV environments, lenses will darken more quickly; in low UV environments, the transition is slower.

• Lens Material and Thickness

Different materials and thicknesses of lenses have varying transition speeds. Generally, thinner lenses transition faster than thicker ones because the photochromic molecules respond more quickly to light changes.

• Brand and Technology

Different brands and technologies of photochromic lenses also vary in transition speed. High-end brands and advanced technologies offer faster transition speeds and more uniform tinting.

• Usage Duration

Over time, the effectiveness and speed of photochromic lenses can decline. It is generally recommended to use photochromic lenses for about three years.

Comparisons of Different Brands and Technologies

The market offers various brands of photochromic lenses, each with unique characteristics in transition speed and performance. Here are comparisons of some common brands and technologies:

Transitions Photochromic Lenses: Transitions is a leading brand in the photochromic lens field, known for its fast transition speed, uniform color, and excellent visual experience under various light conditions. The latest Transitions Signature GEN 8 technology further enhances transition speed and durability.

HOYA Photochromic Lenses: HOYA, a well-known optical company, also offers excellent performance in transition speed and functionality with its Sensity series lenses that can quickly transition within seconds and maintain stable color under different light conditions.

ZEISS Photochromic Lenses: ZEISS, another giant in the optical field, provides photochromic lenses with fast transition speeds, durability, and outstanding visual effects. ZEISS Photofusion technology ensures quick transitions to dark and transparent states.

Essilor Photochromic Lenses: Essilor’s photochromic lenses are also favored by users. Its unique Crizal Transitions technology not only offers fast transitions but also includes anti-glare, UV protection, and other multi-functional features.

Photochromic lenses are a high-tech, multifunctional type of eyeglass lens that can automatically adjust their color based on changes in the surrounding light, providing a comfortable visual experience and comprehensive protection. While there are slight differences in transition speeds among different brands and technologies, modern photochromic lenses typically complete the transition process within a few seconds to a few minutes, meeting the needs of most users.

When choosing photochromic lenses, consider factors such as brand, technology, usage environment, lens material, and additional features to find the most suitable type. With ongoing technological advancements, the performance and functionality of photochromic lenses will continue to improve, offering consumers an even more comfortable and convenient visual experience.

FAQs

Q1: Can I speed up the process?

There is no way to “manually” speed up the transition, but choosing the right lens type and taking care of them can help maintain optimal performance. Regularly replacing older lenses (every 2-3 years) is also recommended, as the responsiveness diminishes over time.

Q2: Why are my photochromic lenses not getting dark enough?

A: Possible reasons: weak UV exposure, old lenses, or low-quality photochromic coating.

Q3: Do photochromic lenses work in winter?

A: Yes, but cold weather makes them darken faster and lighten slower.

Q4: Can I get photochromic lenses in prescription sunglasses?

A: Yes, but they won’t get as dark as dedicated sunglasses.

Q5: How long do photochromic lenses last?

A: Typically 2-3 years before the reaction slows down.