red safelight filter
/ˈɹɛd ˈʌniən/
n
English · red safelight filter中文 · 红色安全灯滤光片Español · filtro rojo de seguridadFrançais · filtre rouge inactinique
意味：Colored filter placed under the lens to frame or focus a black and white image directly onto photographic paper without exposing it.