LED example in "Using Multimeter"

Thread Starter

alisonken1

Joined Apr 2, 2007
1
In the example of using a multimeter to display voltage -
Using a Voltmeter, you use the example of an LED converting light into voltage.

From my understanding of LED's, the reason they are called LED's are the full spelling of the acronym: Light Emitting Diode. LED's convert current into light (hence, the word "Emitting" in the acronym).

It is my understanding that Light Sensing Diode's are what you would be using to convert the light into electricity (which is what the chapter is showing - how to read voltage in a multimeter). Another option would be using a solar cell to convert light into voltage (typical solar cells are 1.5-2.0v at low milliamp rating).
 

hgmjr

Joined Jan 28, 2005
9,029
Indeed an LED can be used as a light detector. Here is another mention of an Led used as light detector . It is by no means the most efficient approach to detecting light but it will work.

I have seen several B.E.A.M. robots that used LEDs as light sensing elements. That is mainly because LEDs are cheap and plentiful.

hgmjr
 

Dave

Joined Nov 17, 2003
6,960
Indeed an LED can be used as a light detector. Here is another mention of an Led used as light detector . It is by no means the most efficient approach to detecting light but it will work.

I have seen several B.E.A.M. robots that used LEDs as light sensing elements. That is mainly because LEDs are cheap and plentiful.

hgmjr
Isn't that essentially a photodiode?

Dave
 

hgmjr

Joined Jan 28, 2005
9,029
Isn't that essentially a photodiode?

Dave
Dave,

That is my thought as well.

I was thinking that the LEDs conductance changes as a function of the light energy rather than generating an electrical voltage out.

hgmjr
 

Dave

Joined Nov 17, 2003
6,960
Dave,

That is my thought as well.

I was thinking that the LEDs conductance changes as a function of the light energy rather than generating an electrical voltage out.

hgmjr
Which IIRC is similar to the photodiode in reverse bias.

In response to the OP, I will have a look at the referenced section later and make more specific comments. If its a case of confusing terminology, even if the existing terminology is correct, then we can look at clearing it up.

Dave
 

Dave

Joined Nov 17, 2003
6,960
Having read the article more thoroughly, I can conclude that it is infact correct and clear. Whilst there is some literal contradiction in the meaning of the name Light Emitting Diode with regards to sensing and responding to a light sourse, the experiment clearly identifies the circumstances when a diode can be used as a "light sensing diode" (in the same manner as a photodiode):

An LED is designed to produce light when powered by a small amount of electricity, but LEDs also happen to generate DC voltage when exposed to light, somewhat like a solar cell. Point the LED toward a bright source of light with your multimeter connected to it, and note the meter's indication... The LED, however, does not rely on an internal "fuel" to generate voltage; rather, it converts optical energy into electrical energy. So long as there is light to illuminate the LED, it will produce voltage.
This experiment clearly demonstrates the ranging functions and applications of LEDs, and hence the e-book article is both technically correct and clear.

I welcome further comments on this.

Dave
 
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