Cold cathodes may also emit electrons by photoelectric emission. The development of the photoelectric photometer allowed precise measurements of magnitude at multiple wavelength intervals. The photovoltaic effect is closely related to the photoelectric effect. This process is called photovoltaic and photoelectric effect. Electrons are ejected from the surface as a consequence of the photoelectric effect. The relation between current and applied voltage illustrates the nature of the photoelectric effect. PV converts light into electric current using the photoelectric effect. The photocurrent may occur as a result of the photoelectric, photoemissive, or photovoltaic effect. A photoelectric device can be either intrinsic or extrinsic. This initiated the concept of photoelectric emission. Other applications include bremsstrahlung and the photoelectric effect. There are also many other photodetectors based on thermal, chemical, quantum, photoelectric and other effects. Thomson also showed they were identical to particles given off by photoelectric and radioactive materials. He also showed they were identical with particles given off by photoelectric and radioactive materials. The densitometer is basically a light source aimed at a photoelectric cell.