I'm afraid I don't understand your question.
what does this replace?
It's called a replacement because it "replaces" the original bulbs supplied with any of the Adorama photo reflectors. Don't make anything of the term "replacement;" it's a light bulb like any other light bulb.
What is the length of the bulb?
The length of the bulb is 8 and 3/4 long. from tip to base.