May be 40 to 50 years ago, someone removed the top metal casing of a 2N3055 and then do some V-I characteristics diagram of the device. The resulting graph is quite textbook result, but with a twist. When the device is moved to a different area of the bench, the V-I characteristics graph came out different. Upon a series of ghost hunting, it was found, the silicon chip is sensitive to light. While it was hidden in the metal casing, this photo-electro effect remains a secret. Later, when LED came along, it was observed that the light emitting device is also sensitive to light.
Photo electroluminescence in the green LED causes a higher forward-drop when shined upon with a flashlight. The excess voltage could be used to trigger the red LED. With a Violet and RoyalBlue combo (405nm/ 420nm), you can even transfer a few100 mW (galvanically isolated). The incident violet light on the RoyalBlue LED manifests as a faint back-glow; this glow can be modulated by loading the blue LED - more load --> less glow :: Useful for reverse communication. I remember a book by Forrest M Mimms where an LED was used as a photodiode :)
There was a circuit in an electronic magazine where a LED was used as transmitter and receiver at the "same" time. The LED was pulsed and whenever the LED was not powered it was used as a photo cell.
The control elements on many lamps contain a light indication of the status. When the lamp is on, the green LED is on. I thought it was a stupid mistake by the serial device manufacturer. But now I tend to think of a sect with stupid rules. Purely technically - a cool trick, with no practical application.
That's not fully correct. There is technical use for this effect: you could use a small status LED to detect ambient light. If you detect light, you know the housing has been opened and the warranty is voided.
en.wikipedia.org/wiki/Photodiode The LED can work as a photodiode, including the direct passage of the supply current. This means that the LED can be used in a voltage divider at the ADC input.
May be 40 to 50 years ago, someone removed the top metal casing of a 2N3055 and then do some V-I characteristics diagram
of the device. The resulting graph is quite textbook result, but with a twist. When the device is moved to a different area of the bench,
the V-I characteristics graph came out different. Upon a series of ghost hunting, it was found, the silicon chip is sensitive to light.
While it was hidden in the metal casing, this photo-electro effect remains a secret.
Later, when LED came along, it was observed that the light emitting device is also sensitive to light.
LED is similar to a solar voltaic. (all the other good explanations were taken below :) )
Photo electroluminescence in the green LED causes a higher forward-drop when shined upon with a flashlight. The excess voltage could be used to trigger the red LED.
With a Violet and RoyalBlue combo (405nm/ 420nm), you can even transfer a few100 mW (galvanically isolated). The incident violet light on the RoyalBlue LED manifests as a faint back-glow; this glow can be modulated by loading the blue LED - more load --> less glow :: Useful for reverse communication.
I remember a book by Forrest M Mimms where an LED was used as a photodiode :)
There was a circuit in an electronic magazine where a LED was used as transmitter and receiver at the "same" time. The LED was pulsed and whenever the LED was not powered it was used as a photo cell.
green LED is used as a sensor when it's not lit, but to the eye (and the camera) it looks like it's always lit?
Die LED wird mit PWM betrieben und während die LED aus ist, wird die Spannung gemessen. Eine LED ist auch eine kleine Solarzelle.
The control elements on many lamps contain a light indication of the status. When the lamp is on, the green LED is on.
I thought it was a stupid mistake by the serial device manufacturer. But now I tend to think of a sect with stupid rules.
Purely technically - a cool trick, with no practical application.
That's not fully correct. There is technical use for this effect: you could use a small status LED to detect ambient light. If you detect light, you know the housing has been opened and the warranty is voided.
deine kamera brithnes und contrast ist einstellen.
en.wikipedia.org/wiki/Photodiode The LED can work as a photodiode, including the direct passage of the supply current. This means that the LED can be used in a voltage divider at the ADC input.