The Michelson-Morley experiment utilized a carbide bicycle lamp as its primary light source, which was suitable for producing a narrow beam. While coherent light sources like lasers were not available at the time, the experiment did not require perfect coherence; a limited range of frequencies was sufficient. The use of a gas discharge tube emitting a line spectrum was also mentioned as a potential alternative for monochromatic light. Concerns about interference effects from a broader frequency range, such as those from an oil lamp, were acknowledged but deemed not problematic in this context. Overall, the choice of light source played a crucial role in the experiment's design and outcomes.
