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Questions tagged [light-emitting-diodes]

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4
votes
4answers
7k views

What determines the forward voltage drop for a diode?

I have always had the idea that the forward voltage drop in a semiconductor diode was related in a simple way to the bandgap energies in the semiconductor. However this is apparently not the case: ...
5
votes
1answer
3k views

Diffraction Pattern on LCD Screen

I was up late working with my red LED headlamp on and when I was looking at the black part of my LCD (Apple Retina Macbook Pro) screen I noticed this interesting diffraction pattern. I'm confused ...
10
votes
1answer
830 views

What's the origin of the four rays that come out of the reflection of candlelight in our TV?

The reflection of a candlelight in our TV shows four emerging rays. The rays vary spatially and periodically and have a repeating pattern of the colors of the rainbow. The further the flame is from ...
6
votes
2answers
943 views

White LEDs and colour perception

I’m very interested in LED lighting and the different spread of wavelengths that are produced compared to other types (like tungsten). Given that a White LED bulb actually produces 3 different peaks ...
21
votes
4answers
3k views

LED conversion efficiency exceed 100%

I have read this article, Which says that conversion efficiency of the LED have exceeded 100%. The results are published in Physical Review Letters In their experiments, the researchers reduced the ...
4
votes
1answer
1k views

Where does a LED use energy other than emitting light?

I have a quantum formula describing what kind of photon should be emitted by an LED depending on its voltage. Of course the colour is depending on the material, but every type of LED also needs its ...
4
votes
2answers
4k views

Can a UV LED cause air ionization?

I am thinking of the high power LEDs at around 250nm wavelength and an output power of some 30mW optical, in continuous mode either divergent beam or focused.
2
votes
2answers
472 views

Why does the light instantly disappear when we switch off the source?

For example i take a box which is completely covered by the most perfect mirrors possible inside and inside that box i have a bulb whose bulb holder is also covered with the most perfect mirrors ...
1
vote
3answers
1k views

Why does the intensity of a LED change as the temperature increases

I am working with an array of LEDs and I am looking into how there properties change as they heat up. One of the things I found out is that the intensity of these the light decreases as the LEDs heat ...
0
votes
1answer
2k views

Experimental measure of light wavelength of a LED or Lamp

First: I've found these questions (Here and Here) about this subject, but i don't think any of them will help me in this case since it was about measure it when you have a beam of light. I'm looking ...
0
votes
1answer
52 views

How do electrons exit LEDs? Aren't they in the valence energy state?

If a conducting electron reduces to the valence band in an LED, where does it get the energy to go back to the conductance band upon leaving the diode so current can flow? I'm confused as to how ...