Question

add a comma or semicolon if needed. otherwise, submit the text without any additional punctuation.
louis-jacques-mandé daguerre and nicéphore niépce invented the first successful photographs in the 1830s. niépces initial effort required eight hours of exposure time daguerres required only twenty or thirty minutes.

Explanation:

The two independent clauses ("Niépce's initial effort required eight hours of exposure time" and "Daguerre's required only twenty or thirty minutes") are being contrasted and should be separated by a semicolon to show the relationship between the two related ideas about the exposure times of their respective efforts. A semicolon is appropriate here instead of a comma because they are two complete sentences (independent clauses) that are closely related in meaning.

Answer:

Louis-Jacques-Mandé Daguerre and Nicéphore Niépce invented the first successful photographs in the 1830s. Niépce's initial effort required eight hours of exposure time; Daguerre's required only twenty or thirty minutes.