(band of visible light around 6500 angstroms)
The R band is the red band of photometric systems,
typically centered round 658nm and a full width at half maximum of 138nm.
R may indicate the band or a filter adhering to the specification.
The letter is also used to indicate the magnitude of the signal
observed through the filter, e.g., citing "R = 1.5".
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UBV photometric system