https://blog.gongquiz.com/2020/11/28/%ed%94%8c%eb%a6%ac%ec%bb%a4-%ea%b2%80%ec%82%acflicker-test%ec%9d%98-%eb%aa%a9%ec%a0%81%ec%9c%bc%eb%a1%9c-%ea%b0%80%ec%9e%a5-%ec%a0%81%ec%a0%88%ed%95%9c-%ea%b2%83%ec%9d%80-%ec%82%b0%ec%97%85/