Optical Filters – Color Filters
I. What are color filters？
Have you ever considered upgrading to anti-blue light lenses when choosing eyeglasses? Are you curious how these lenses reduce eye strain from long hours of using electronic devices?
Figure 1: Blue light filter diagram [1]
In fact, lenses have multiple layers of coating that selectively block blue light, reducing the amount of blue light that enters your eyes. This helps alleviate eye strain during long hours of using electronic devices or engaging in outdoor activities.
Figure 2: Blue light filter spectrum diagram (LED screens and sunlight) [2]
Selecting the specific lens material and optical designs control certain wavelengths of light to pass through while reflecting unwanted wavelengths. This reduces glare, improves contrast, and enhances visual comfort, making it ideal for outdoor activities.
Figure 3: Color filter lens color range and suitable environments [1]
II. Design Principle of All-Dielectric Reflective Color Filters
1. Wavelength and Color of Light
The colour of spectrum is determined by its wavelength. The visible radiation ranges between 380 and 750 nm. Figure 4 illustrates the corresponding colour to each specific wavelength of the spectrum.
Choosing the optical design, material, and filter colour against the application. For example, a red filter reflects most non-red light and only allows red light (620~750nm ) to pass while reducing glare and enhancing visual contrast.
Figure 4: Sunlight spectrum and corresponding visible light wavelengths [3]
2. Material Selection
Different materials not only affect the color and optical performance of the filter but also impact its durability, cost, and how it handles different types of light. There are three main aspects：
• High/Low Refractive Index Materials：The transparency or reflectivity of the coupling film filters light at specific wavelengths.
• Material Performance：Factors such as transmission rate, reflectance, absorption rate, etc… directly affect colour accuracy and filtering performance.
• Durability and Stability：External factors including temperature changes, humidity, UV light, etc… challenge the ability of weather-resistant and stable.
3. Multi-Layer Coating Design
Dah Young's design for the Full Dielectric Film Reflective Color Filter utilizes a c-stack and a quarter-wavelength film stacking concept, tailored to specific target wavelengths. When light enters the filter, selective interference occurs for different wavelengths, reflecting the desired color range while allowing other wavelengths to pass through, thereby achieving the goal of color filtering.
By adjusting the target wavelength, different light colors can be selectively filtered. As shown in Figure 5, changing the design wavelength from 720 nm to 660 nm shifts the reflected color from red to yellow.
Figure 5: Adjusting the target wavelength to modify the filter design [4]
Increasing the number of layers enhances the reflection effect. Additionally, using quarter- and half-wavelength film stacking creates a mixed color effect by reflecting broader or multiple wavelength ranges. In Figure 6, adjusting the design to reflect blue and violet light results in a pink color filter.
Figure 6: Using quarter-wavelength and half-wavelength film stacking designs to adjust the filter design [4]
III. Practical Applications
This multi-layer coating structure not only precisely controls the light transmission properties of the filter but also efficiently filters colors. By applying this design concept to the surface of sunglasses or ski goggles, it enhances color vibrancy and improves visual contrast。
Figure 7: Different color filter lens designs applied to ski goggles [5]
In addition, the coating provides scratch resistance, durability, and water- and dirt-repellent properties, keeping the lenses clean and maintaining optimal visual performance over time.
Most importantly, DAH YOUNG VACUUM's coating has passed environmental tests and is certified by customers, ensuring stability and reliability in different environments.
Figure 8: The lens passes environmental tests and receives customer certification [6]
IV. Reference
[1] 愛·鏡. (2023).如何選購你所需要的鏡片種類與規格？
Retrieved February 10, 2025, from（https://www.eyejing.com/encyclopedia-detail/lens-type/）
Retrieved February 10, 2025, from（https://oledbetterlife.weebly.com/29986216972017132057.html）
[3] verilux. (2011). UVC Light & UV Light Sanitizers.
Retrieved March 02, 2025, from（https://verilux.com/pages/uvc-light-uv-light-sanitizers）
[4] Dah Young Vacuum Equipment Co., Ltd.(2020). Full Dielectric Film Reflective Color Filter.
Retrieved February 10, 2025, from（https://zh-tw.dahyoung.com/list/cate-258732.htm）
Retrieved March 03, 2025, from（https://zh-tw.dahyoung.com/news-detail/new-premium-decorative-coating-series-for-sunglasses-goggles-high-quality-coating-technology-that-enhances-both-color-and-performance.htm）
[6] Dah Young Vacuum Equipment Co., Ltd.(2024).The Activated Reactive Magnetron Sputtering (ARMS) coating machine, developed by Dah Young specifically for the sports eyewear industry.
Retrieved March 03, 2025, from（https://zh-tw.dahyoung.com/news-detail/technical-journal-the-activated-reactive-magnetron-sputtering-arms-coating-machine-developed-by-dah-young-specifically-for-the-sports-eyewear-industry-2.young-specifically-for-the-sports-eyewear-industry-2.htm）