"I have long hair" 用英语表达就是 "I have long hair"。
关于"长发"这个词，它来源于英语单词"hair"，"hair"本身就是指头发的意思，所以直接说"long hair"就可以表示长发。
如果你想表示长发是黑色的，可以说：
"I have black long hair"
例句:
"She has long, dark hair" (她有长长的深色头发)
"He's growing his hair out and it's getting really long" (他在让头发长长，现在已经很长了)
翻译
"她有长长的深色头发" 可译为 "She has long, dark hair."
"他在让头发长长，现在已经很长了" 可译为 "He's growing his hair out and it's getting really long."