ENERGY_BAND is no longer used at all for the lightcurve and spectrum objects. For lightcurve and spectrum, the default value is [0.,0.] and should not be changed.
For lightcurve, use LTC_ENERGY_BAND to set energy bands.
For spectrum, use SP_ENERGY_BINNING to set energy bands.
For image, use ENERGY_BAND to set the min, max of the energies to use, but see IM_ENERGY_BINNING and EB_INDEX for more options for setting energy bands for images.