cyamamot@nunki.usc.edu (Cliff Yamamoto) (01/04/89)
In message <3258@hermes.ai.mit.edu> (John Purbrick) writes: >The original article was about powerful visible LEDs, rated in candelas, which >is normal for visible light. How does this compare to infrared LEDs, which are >usually rated in terms of total watts and watts/sterradian (watts radiated >into a unit angle at the brightest point)? Are the visible lamps catching up >to the IR ones? > >Note: Visible light, measured in candelas, is nonlinearly related to actual >power, because the candela takes into account the varying response of the eye >to different colors. An infrared lamp rates 0 candelas, although most Hewlett- >Packard IR LEDs seem to be near-infrared and emit a small amount of visible >light too. "Aids alignment", as the catalog says. ^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^ Can someone explain how to compare IR diodes with visible LEDs? Is the radiant intensity "Ie" parameter *INDEPENDENT* of whether a diode emits IR or visible light? For example in the HP catalog it says : Ie = Iv / nv where : Ie = radiant intensity in watts per steradian lv = luminous intensity in candelas nv = luminous efficacy in lumens per watt Although the Ie is not specified, the 1000mcd HLMP-4101 has : Iv = 1000mcd (1 candela) nv = 80 lm/W which implies that Ie = 1/80 = 12.5 milliwatts/steradian However the HEMT-3301 IR emitter has Ie = 4.0 milliwatts/steradian 1) Can I infer from this radiant intensity parameter that the HLMP-4101 produces a "brighter" output than the HEMT-3301? In otherwords, if I had some sort of optical "spectrum analyzer", would the peak at 650 nm for the 4101 be higher than the peak at 940 nm for the 3301? 2) Are silicon photodetectors more sensitive at 650 nm than at 940 nm? If these 1000mcd red LEDs are truly "brighter" than IRs, would it be possible to replace an IR emitter with a "bright" red LED in a remote control application? As long as the receiver uses a photodetector that is equally sensitive at red as it is with IR would the range be increased? Thanks in advance for any information! Cliff Yamamoto Internet : cyamamot@castor.usc.edu castor!cyamamot@oberon.usc.edu cyamamot@nunki.usc.edu cyamamot%nunki.usc.edu@oberon.usc.edu