What is the traditional Chinese character "Lei Min" next to the word "light"

This is Lu's calligraphy:

Lu (China surname) generally refers to Lu surname. Lu surname is one of the surnames in China, and it is a typical multi-ethnic and multi-origin surname, which mainly comes from the changes of Jiang surname, Ji surname and minority surnames. It was Lu's ancestors in the Spring and Autumn Period. Lu ranked 167 among the hundred surnames in Song Dynasty.