code: def luminosity_within_ellipse_in_units(self, major_axis : dim.Length, unit_luminosity='eps', kpc_per_arcsec=None, exposure_time=None):
          
          if self.has_light_profile:
              return sum(map(lambda p: p.luminosity_within_ellipse_in_units(major_axis=major_axis, unit_luminosity=unit_luminosity,
                                                                            kpc_per_arcsec=kpc_per_arcsec, exposure_time=exposure_time),
                             self.light_profiles))
          else:
              return None
docs: Compute the total luminosity of the galaxy's light profiles, within an ellipse of specified major axis. This 
          is performed via integration of each light profile and is centred, oriented and aligned with each light
          model's individual geometry.
  
          See *light_profiles.luminosity_within_ellipse* for details of how this is performed.
  
          Parameters
          ----------
          major_axis : float
              The major-axis radius of the ellipse.
          unit_luminosity : str
              The units the luminosity is returned in (eps | counts).
          exposure_time : float
              The exposure time of the observation, which converts luminosity from electrons per second units to counts.