An important part of an optical system is to convert light to a signal that then can be analyzed or stored. The basic principles of using a photon detector involve detection of light and converting the light intensity signal to current or voltage via an amplifier. The absorbed photons change the electronic characteristic of the detector. Photon detectors are generally much more sensitive than thermal detectors. Thermal detection is achieved when incident optical radiation is absorbed, causing a rise in the temperature of the detector element, which is then converted to an electrical signal. When attempting to detect extremely low levels of light, standard photodiodes may not be sufficient, because to obtain an electrical signal of a measurable level, the signal has to be amplified. To measure total optical power from a source that has a wide range of angles an apparatus called an integrating sphere can be used to collect the total light emission.