What Light Source Was Used in the Michelson-Morley Experiment?

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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.
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Since this experiment was done long before lasers were invented, what did they use as a coherent light source? All the explanations of the experiment I can seem to find skip this detail and I am curious.
 
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They didn't need a coherent light source. A narrow beam sufficed.
 
I suppose the important bit wouldn't be the coherent bit, but having a light source with a limited range of frequencies so that the change in intensity due to the change in interference in one wavelength wasn't canceled out by an opposite change in intensity from other wavelengths interfering differently. A light source like an oil lamp would have too large a range of frequencies for the interference effects to not wash each other out wouldn't it?
 
I don't know what they used as a light source, but whatever they used, the problem you raised didn't seem to be an issue.
 
For monchromatic light something like a gas discharge tube that emits a line spectrum would do the job.
 
They used a carbide bicycle lamp for the experiments. They sometimes used a sodium-vapor lamp to help set up.
 

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