What is the difference between 華誕 and 誕辰? Both 華誕 and 誕辰 are more respectful ways of saying 生日 (birthday).

For 華誕, I have seen: "最高元首華誕", "蘇丹華誕", "日本皇華誕".

For 誕辰, I have seen: "國父誕辰", "先知默罕默德誕辰".

Sometimes, within a text, I see 華誕 being consistently used for the birthday of a particular person, and 誕辰 being used exclusively for the birthday of another person. So I wonder: is there a convention for selecting one over the other for particular "types" of people, or is selection completely arbitrary and always interchangeable?
都是一个意思，一般华诞表示国家的生日，是很美妙的事件。诞辰没有华诞那么宏大美好，但也有赞美的意思。