Dember effect
In physics, the Dember effect is when the electron current flowing from a cathode 
subjected to both illumination and a simultaneous electron bombardment is greater than the sum of the photoelectric current 
and the secondary emission current 
.
Discovered by Harry L. Dember (1882-1943) in 1925, this effect is due to the sum of the excitations of an electron by two means: photonic illumination and electron bombardment (i.e.the sum of the two excitations extracts the electron). In Dember’s initial study, he referred only to metals; however more complex materials have been analyzed since then.
The photoelectric effect due to the illumination of the metallic surface extracts electrons (if the energy of the photon is greater than the extraction work) and excites the electrons which the photons haven’t got the energy to extract.
In a similar process, the electron bombardment of the metal both extracts and excites electrons inside the metal.
If we consider 
a constant and increase 
it can be observed that 
has a maximum of about 150 times .
On the other hand, considering I_2 a constant and we increase the intensity of the illumination the , supplementary current, tends to saturate. This is due to the usage in the photoelectric effect of all the electrons excited (sufficiently) by the primary electrons of .
The Dember effect has no relation to the financial markets "December effect". See January effect