Parses one or more spectra from a TriOS RAMSES `.dat` text file. Each spectrum is preceded by a `Comment` header line and terminated by a `[END]` marker. Data rows contain three whitespace-separated fields: index, wavelength (nm), and spectral radiance (mW m\(^{-2}\) nm\(^{-1}\) sr\(^{-1}\)). Radiance values are converted to W m\(^{-2}\) nm\(^{-1}\) sr\(^{-1}\). Negative instrument values are preserved; no clipping or other preprocessing is performed by this low-level reader.