I always have a doubt when someone says that light is emitted by only certain transitions of electron but not by all of them. If an electron jumps from a higher energy orbit to a low energy orbit, is the energy difference released only in the form of a photon packet or does it release in any other forms of energy? Now, I say that a material can emit light in so and so wavelength, does it mean that the object is transparent to those wavelengths and other wavelengths are just absorbed to generate heat?
The energy freed by the transition from a higher to a lower energy state can be released by various other mechanisms (which observe conservation laws) in addition to the emission of a photon. An example is the Auger effect, where the energy is released by the kinetic energy of another emitted electron. In solids (semiconductors), the transition energy is often released by a photon plus a phonon which is necessary for momentum conservation.
Postscript: Upon suggestion of @CountTo10 I add some links I have found. Here a lecture on radiative transitions mentioning also some non-radiative ones in gases https://legacy.wlu.ca/documents/37121/NotesCh4.pdf