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VT83CT 数据表(PDF) 29 Page - PerkinElmer Optoelectronics |
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VT83CT 数据表(HTML) 29 Page - PerkinElmer Optoelectronics |
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29 / 76 page  24 Application Notes—Photoconductive Cells LED Light Sources APPLICATION NOTE #4 Spectral Matching of LEDs and Photoconductive Types Since light sources and light detectors are almost always used together the designer must take into consideration the optical coupling of this system or the ability of the detector to “see” the light source. In order to have good optical coupling between the emitter and the conductor the spectral output of the light source must, to some degree, overlap the spectral response of the detector. If the design involves the use of a light source with a broad band spectral output the designer is assured that the photocell will have good response to the light. This may not be the case when an LED light source is employed. LEDs emit their light within a very narrow spectral band so that they are often considered to be emitting at only on (peak) wavelength. Spectral matching factors were calculated for a number of different LEDs and the photoconductor material types manufactured by PerkinElmer. Each matching factor was derived by multiplying the detector response curves by the LED spectral output curve and then measuring the resulting area. The LED/photocell matching factors listed are independent of power output from the LEDs. In order to get a real feel on how well any LED/ photocell pair couple together, the power output from the LED at a particular forward drive current must be considered. Normalized LED/Photocell Matching The intensity of the light being emitted by visible LEDs is often given in units of millicandela. Millicandela is photometric unit of measure which assumes the human eye as the detector. For most detectors other than the human eye the most convenient system for measurement is the radiometric system. Listed below is the typical light power output of some LEDs measured at two different forward drive currents. Note that LEDs of a given type can show a 5:1 manufacturing spread in power outputs. LED Type Color λ P GaP GREEN 569 nm GaAsP/GaP YELLOW 585 nm GaAsP/GaP ORANGE 635 nm GaAsP/GaAs RED 655 nm AIGaAs RED 660 nm GaP/GaP RED 697 nm GaAIAs INFRARED 880 nm GaAs INFRARED 940 nm LED Type λ P (nm) Type Ø Material Type 3 Material GaP 569 39% 40% GaAsP/GaP 58 60% 52% GaAsP/GaP 635 49% 38% GaAsP/GaAs 655 31% 27% AIGaAs 66 31% 27% GaP/GaP 697 47% 31% GaAIAs 880 — — GaAs 940 — — LED Type Color λ P (nm) Power Output If = 1 mA If = 10 mA GaP GREEN 569 nm 1.2 µW 24.1 µW GaAsP/GaP YELLOW 585 nm 0.3 µW 26.2 µW GaAsP/GaP ORANGE 635 nm 3.2 µW 101.9 µW GaAsP/GaAs RED 655 nm 6.2 µW 102.1 µW AIGaAs RED 660 nm 33.8 µW 445.1 µW GaP/GaP RED 697 nm 54.3 µW 296.2 µW GaAIAs INFRARED 880 nm 76.8 µW 1512.3 µW GaAs INFRARED 940 nm 35.5 µW 675.0 µW |
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