{"id":3540,"date":"2025-09-13T12:36:13","date_gmt":"2025-09-13T04:36:13","guid":{"rendered":"https:\/\/www.taichungbro.com\/?p=3540"},"modified":"2025-09-13T12:36:16","modified_gmt":"2025-09-13T04:36:16","slug":"optical-filter","status":"publish","type":"post","link":"https:\/\/www.taichungbro.com\/en\/2025\/09\/13\/optical-filter\/","title":{"rendered":"Why does a blood moon turn the sky red? From astronomical wonders to optical filters."},"content":{"rendered":"<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-wide\"\/>\n\n\n\n<div class=\"wp-block-rank-math-toc-block\" id=\"rank-math-toc\"><h2>Table of Content<\/h2><nav><ul><li class=\"\"><a href=\"#\u8840\u6708\u7684\u5149\u5b78\u539f\u7406\uff1a\u745e\u5229\u6563\u5c04\u8207\u6298\u5c04\u6548\u61c9\">The optical principle of the blood moon: Rayleigh scattering and refraction effect<\/a><\/li><li class=\"\"><a href=\"#\u5f9e\u8840\u6708\u8ac7\u5230\u5149\u5b78\u6ffe\u5149\u7247\uff1a\u5de5\u696d\u754c\u7684\u61c9\u7528\">From Blood Moon to Optical Filters: Industrial Applications<\/a><\/li><li class=\"\"><a href=\"#\u934d\u819c\u6280\u8853\uff1a\u8b93\u5149\u5b78\u5143\u4ef6\u66f4\u9ad8\u6548\">Coating technology: making optical components more efficient<\/a><\/li><li class=\"\"><a href=\"#\u534a\u5c0e\u9ad4\u8207\u7cbe\u5bc6\u6aa2\u6e2c\u4e2d\u7684\u5be6\u969b\u6578\u64da\">Real-world data in semiconductors and precision testing<\/a><\/li><li class=\"\"><a href=\"#\u822a\u592a\u8207\u5929\u6587\u89c0\u6e2c\u7684\u5ef6\u4f38\u61c9\u7528\">Extended applications of space and astronomical observation<\/a><\/li><\/ul><\/nav><\/div>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-wide\"\/>\n\n\n\n<p class=\"wp-block-paragraph\">The term &quot;blood moon&quot; has recently resurfaced as a trending topic. A blood moon is a spectacular astronomical phenomenon; during a total lunar eclipse, the normally silvery-white moon turns crimson, resembling a giant fireball hanging in the night sky. For the general public, the blood moon represents romance and mystery; however, for the scientific and industrial communities, the underlying optical principles are closely related to many applications in our daily lives. This article will begin by explaining the formation principles of the blood moon, guiding readers through optical filters, coating technologies, and related industrial applications, and exploring how these technologies support the development of the semiconductor, precision testing, and even aerospace industries.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u8840\u6708\u7684\u5149\u5b78\u539f\u7406\uff1a\u745e\u5229\u6563\u5c04\u8207\u6298\u5c04\u6548\u61c9\">The optical principle of the blood moon: Rayleigh scattering and refraction effect<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A blood moon is formed during a total lunar eclipse. When the Earth is positioned between the Sun and the Moon, it blocks direct sunlight from reaching the Moon. Theoretically, the Moon should be completely dark, but in reality, we can still see a red moon. This is because when sunlight passes through the Earth&#039;s atmosphere, blue light, due to its shorter wavelength, is scattered away, leaving only red and orange light to penetrate and refract into the Earth&#039;s shadow, illuminating the lunar surface and making the moon appear red. This phenomenon is similar to the reddish hue of the sky at sunset, a typical example of Rayleigh scattering and light refraction.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u5f9e\u8840\u6708\u8ac7\u5230\u5149\u5b78\u6ffe\u5149\u7247\uff1a\u5de5\u696d\u754c\u7684\u61c9\u7528\">From Blood Moon to Optical Filters: Industrial Applications<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The key to the blood moon phenomenon lies in the &quot;selective transmission and scattering of light.&quot; This principle is most commonly used in industry for optical filters. The function of a filter is to allow only specific wavelengths of light to pass through, while absorbing or reflecting the rest. For example:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>In semiconductor inspection equipment, filters can separate light of different wavelengths, assisting optical inspection systems in identifying wafer defects.<\/li>\n\n\n\n<li>In laser processing, specialized filters can filter out dangerous wavelengths, ensuring the safety of operators.<\/li>\n\n\n\n<li>In medical optics, such as endoscopes or laser treatment devices, filters can enhance the required spectrum to improve image quality or treatment accuracy.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">The blood moon reminds us that optical effects in nature are actually closely linked to industrial optics technology.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u934d\u819c\u6280\u8853\uff1a\u8b93\u5149\u5b78\u5143\u4ef6\u66f4\u9ad8\u6548\">Coating technology: making optical components more efficient<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Besides optical filters, another indispensable optical application is coating technology. When we need to control the reflection, transmission, or absorption of light, we often coat the surface of glass or crystal with multiple thin films. These coatings are often on the nanometer scale in thickness, allowing for precise manipulation of light interference and transmission efficiency. For example:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Anti-reflective coating (AR coating): Commonly used in camera lenses or telescopes, it can reduce light reflection and improve image clarity.<\/li>\n\n\n\n<li>High reflectivity coating (HR coating): applied to laser mirrors to improve energy efficiency.<\/li>\n\n\n\n<li>Band-pass filter coating: only allows specific wavelengths to pass through. For example, pulse oximeters use red and infrared light bands for measurement.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">If we use the blood moon as a metaphor, Earth&#039;s atmosphere is like a natural &quot;filter&quot; and &quot;filter coating,&quot; allowing only red wavelengths to enter the shadow region.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u534a\u5c0e\u9ad4\u8207\u7cbe\u5bc6\u6aa2\u6e2c\u4e2d\u7684\u5be6\u969b\u6578\u64da\">Real-world data in semiconductors and precision testing<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">In semiconductor manufacturing, optical inspection is a crucial step in ensuring quality. Below is an example of design parameters for a filter application:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Application areas<\/th><th>Center wavelength of the filter (nm)<\/th><th>Passband width (nm)<\/th><th>Blocking optical density (OD)<\/th><\/tr><\/thead><tbody><tr><td>Wafer Defect Detection<\/td><td>532<\/td><td>10<\/td><td>6<\/td><\/tr><tr><td>Laser alignment system<\/td><td>633<\/td><td>5<\/td><td>5<\/td><\/tr><tr><td>Blood oxygen sensing (medical)<\/td><td>660\/940<\/td><td>20<\/td><td>4<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">These data represent how engineers, when designing optical systems, precisely control the wavelength of light according to application requirements, much like how the Earth&#039;s atmosphere &quot;selects&quot; red light for us.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u822a\u592a\u8207\u5929\u6587\u89c0\u6e2c\u7684\u5ef6\u4f38\u61c9\u7528\">Extended applications of space and astronomical observation<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A blood moon is itself a form of astronomical observation. In the aerospace and astronomy industries, optical filters and coating technologies are crucial. For example, space telescopes need to separate infrared, visible, and ultraviolet light; these filters and coating components must withstand extreme temperature changes and even resist radiation damage. The challenges behind this are far more stringent than those of camera lenses used in everyday life.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Meanwhile, the industry often feeds back the demand for astronomical observations to the manufacturing sector, driving upgrades in optical glass, single-crystal materials, and precision coating equipment. It can be said that from astronomical wonders like the &quot;blood moon&quot; to high-end industries like &quot;semiconductor production lines,&quot; they all rely on the same set of fundamental optical principles.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p class=\"wp-block-paragraph\">Although a blood moon is a brief astronomical phenomenon, it reminds us that the optical effects of nature have long been transformed and applied by humankind in industry and daily life. From optical filters to coating technology, from semiconductor testing to medical sensing, and even extending to aerospace and astronomical research, all these technologies rely on the precise control of light wavelengths. The next time you look up and see a blood moon, you might realize that this beautiful red moon is actually intricately connected to your phone&#039;s camera lens, medical equipment, and even the testing machines in a semiconductor factory.<\/p>\n\n\n\n<div style=\"height:var(--wp--preset--spacing--30)\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-wide\"\/>\n\n\n\n<h5 class=\"wp-block-heading has-text-align-center\" id=\"\u60f3\u4e86\u89e3\u6709\u95dc\u7ba1\u87ba\u7d0b\u3001\u76f4\u87ba\u7d0b\u3001\u9310\u87ba\u7d0b\u3001\u5c3a\u5bf8\u8868\u793a\u3001\u82f1\u5236\u7ba1\u87ba\u7d0b\u3001\u516c\u5236\u7ba1\u87ba\u7d0b\u7684\u77e5\u8b58\u55ce\uff1f-\u5ef6\u4f38\u95b1\u8b80\uff1a\u300a\u7ba1\u87ba\u7d0b\u767e\u767e\u7a2e-\u4f60\u90fd\u8a8d\u8b58\u55ce-\u300b\">Want to learn about components related to image sensing and processing? <br>Further Reading :<a href=\"https:\/\/www.taichungbro.com\/en\/2025\/02\/04\/image-processing\/\" data-type=\"link\" data-id=\"https:\/\/www.taichungbro.com\/2025\/02\/04\/image-processing\/\">What are the differences between CMOS and CCD? Demystifying the two giants of image processing.<\/a><\/h5>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-wide\"\/>\n\n\n\n<div style=\"height:11px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>","protected":false},"excerpt":{"rendered":"<p>A blood moon is a spectacular astronomical phenomenon, but the underlying optical principles have wide applications in industry and daily life. This article takes you from the Rayleigh scattering and refraction effects of the blood moon to optical filters and coating technologies, exploring their important roles in semiconductor inspection, medical optics, and aerospace. When you look up at the blood moon again, you may discover the close connection between it and industrial technology.<\/p>","protected":false},"author":2,"featured_media":3542,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[45],"tags":[382,385,381,383],"class_list":["post-3540","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industrial-knowledge","tag-382","tag-385","tag-381","tag-383"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/posts\/3540","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/comments?post=3540"}],"version-history":[{"count":0,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/posts\/3540\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/media\/3542"}],"wp:attachment":[{"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/media?parent=3540"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/categories?post=3540"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/tags?post=3540"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}