  We highlight a physical effect that is often not considered that impacts the
calculation of model spectra of planets at secondary eclipse, affecting both
emission and reflection spectra. The radius of the emitting surface of the
planet is not merely one value measured from a transit light curve, but is
itself a function of wavelength, yet it is not directly measurable. At high
precision, a similar effect is well-known in transit "transmission
spectroscopy" but this related effect also impacts emission and reflection. As
is well-appreciated, the photospheric radius can vary across $\sim$4-8
atmospheric scale heights, depending on atmospheric opacity and spectral
resolution. This effect leads to a decreased weighting in model calculations at
wavelengths where atmospheric opacity is low, and one sees more deeply into the
atmosphere, to a smaller radius. The overall effect serves to mute emission
spectra features for atmospheres with no thermal inversion but to enhance
features for atmospheres with a thermal inversion. While this effect can be
ignored for current \emph{Hubble} observations, it can lead to
wavelength-dependent 10-20\% changes in planet-to-star flux ratios in the
infrared at $R\sim~200-1000$ (readily achievable for JWST) for low-gravity hot
Jupiters, although values of 5\% are more typical for the population. The
effect is mostly controlled by the ratio of the atmospheric scale height to the
planet radius, and can be important at any planetary temperature. Of known
planets, the effect is largest for the cool "super-puffs" at very low surface
gravity, where it can alter calculated flux ratios by over 100\%. We discuss
complexities of including this photospheric radius effect in 1D and 3D
atmosphere models.
