Radiant flux

Radiant flux measurement method

For radiant flux, the full radiant output power is measured when a specified forward current flows into the LED. To measure the radiant power emitted in the horizontal direction, a reflector is provided so that the entire radiant power emitted in every direction from the LED can be detected by a photodiode placed in front of the LED.

Radiant sensitivity

Radiant sensitivity is the photoelectric current generated when a photoactive surface is struck by light at a given wavelength. It is defined as the current divided by the incident radiant power, and expressed in A/W (amperes per watt). See cathode radiant sensitivity.

Reach-through structure

A structure (example: N+ -P -π -P+ layer) whose impurity concentration is not uniform, and is formed in a region near the PN junction boundary in an APD. The π-layer serves as the light absorption region and carriers generated here are multiplied in the P-layer. The APD is used with a high reverse voltage applied so that the π-layer is depleted (reach-through) in order to enhance the speed. This structure is therefore called the reach-through type.

Readout noise - CCD

Readout noise is independent of the amount of light exposure. It is amount of noise generated by the CCD. It is independent of light level or dark current.

Red/white ratio - Photomultiplier tube

Red/white ratio is used for comparing the sensitivity of photomultiplier tubes having a spectral response extending to the near infrared region. Like blue sensitivity index, the red/white ratio is also measured with the measurement system used for cathode luminous sensitivity, but a red to infrared filter is interposed. Red/white ratio is defined as the ratio of the cathode sensitivity measured with a red to infrared filter, as compared with the cathode luminous sensitivity when measured without a filter.

Reflector type

Xenon flash lamps are equipped with a built-in reflecting mirror, which allows, as much as 4x the amount of light to be obtained as that from conventional lamps. Two types of reflecting mirror are available for selection:

  • Converging: rays of light are reflected or bent towards each other
  • Collimating: every ray of reflected light is parallel to the others

Reverse voltage max. (VR max)

Applying a reverse voltage to a device triggers a breakdown at a certain voltage and causes severe deterioration of the device's performance. Therefore the absolute maximum rating is specified for reverse voltage at the voltage somewhat lower than this breakdown voltage. The reverse voltage should not exceed the maximum rating, even instantaneously.

Rise time

The rise time is the time required for the output to rise from 10% to 90% of the maximum output value (steady-state value) in response to input of step-function light.