The tag has no usage guidance.

learn more… | top users | synonyms (1)

9
votes
2answers
153 views

Spatial coherence of SLED light (width of active region?)

As far as I know, super-luminescent diodes (a.k.a. SLEDs) have a very similar structure to laser diodes, except that the front faces of the active region are tilted to prevent the sort of reflections ...
3
votes
1answer
93 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 ...
0
votes
1answer
75 views

What's the difference between stimulated and spontaneous emission in lasers and diodes?

I know that an LED emits light by spontaneous emission. To get more coherent and Monochromatic light, we should use a laser. What is the reason that laser light is the most coherent and ...
0
votes
1answer
25 views

Direct bandgap semiconductor reaction to heat. Produce light?

In an indirect bandgap semiconductor if you apply heat the number of free electrons increases, conductivity increases, and the bandgap decreases. In a direct bandgap semiconductor is there any ...
0
votes
1answer
27 views

How to configure two infrared light to produce two different intensity

I have two infrared illuminators that have the same properties (same wavelength, same number of leds, same angles, same max voltage and amperage). suppose that these illuminators are attached at the ...
3
votes
0answers
261 views

Where does an 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 ...
3
votes
0answers
687 views

Increase in Wavelength of an LED immersed in liquid nitrogen

"Hi, I've been working on an experiment where I dip LEDs into liquid nitrogen and note the color change. All online sources I've seen predict that the wavelength of the light emitted by the LED will ...
2
votes
0answers
35 views

Is it possible to use a tapered fiber to collimate a single-mode light beam?

I would like to collimate a light beam stemming from a single-mode LED source. As the source is pretty big (a few millimeters), collimation with a single lens gives a bad result, i.e. a quite ...
2
votes
0answers
57 views

Interpretation of the diode constant in a LED

For a real diode the current as function of the potential difference between its terminals (for big enough voltage) is given by: $$I=A e^{\frac{eV-E}{\eta k_B T}} \tag{1}$$ So in the case of LEDs ...
2
votes
0answers
135 views

Formulas for Haitz's law?

The Nobel Prize in Physics 2014 is for LED. There is a related Haitz's law: ...every decade, the cost per lumen (unit of useful light emitted) falls by a factor of 10, and the amount of light ...
1
vote
0answers
13 views

why are triplet excitons more tightly bound than singlet?

In organic light emitting diodes, the Jablonski diagrams always show he T1 states to be lower in energy to the S1 states. They are also declared to be more tightly bound as a result. I don't ...
1
vote
0answers
21 views

What size aluminum foil capacitor would power an LED?

Inspired by this video where a $9 \mu F$ capacitor is made from aluminum foil, if I had students put this together in a classroom, one question I would have is what would it take to have this power an ...
1
vote
0answers
295 views

Variable wavelength LED

Does there exist a type of LED (or other type of light source) that can change it's wavelength depending on the current/voltage it receives on a second wire? If not, would something like this even be ...
1
vote
0answers
46 views

Where does the reverse current come from in a organic semiconducting diode?

Unlike traditional inorganic diodes, organic semiconducting materials hold few thermally exited free carriers under room temperature, so the reverse current should be small if pinholes of the films is ...
0
votes
0answers
13 views

LCD vs. LED heating issues

Does the color of the picture influence the temperature of the display, and does this depend on the type of the display (AMOLED/LCD)? As far as I understand this can be true for LED displays since ...
0
votes
0answers
33 views

Green LED Forward Voltage

Yesterday in lab, we were asked why all of our green LED had large forward voltage than expected. We expected for the forward voltage to be at around 2.1V as according to hf=Egap=eV. Yet, we ...
0
votes
0answers
30 views

How to determine Irradiance (W/m^2) at surface due to LED luminous intensity (mcd)

Thanks in advance for the help, I do not think this is a duplicate questions although there are some related discussions. While I'm mainly interested in the generic solution, my specific question ...
0
votes
0answers
20 views

Transmittance of yellow light through blue substance

I am performing an experiment in which I flash an LED-light through a substance with different opacities and do voltage measurements over a photoresistor on the other side. When I decrease the ...
0
votes
0answers
26 views

How to calculate apex angle of sun shining on the Earth

I'm trying to compare the brightness of various LEDs to the average brightness of natural daylight. LEDs are rated in terms of candelas whereas the Sun is measured in terms of lumens, so I need to ...
0
votes
0answers
24 views

Do LEDs that require a higher forward voltage (at the same forward current) also use more power?

Why do some LEDs require a higher forward voltage than others for the same forward current? Is it defects, band-gap, etc? Does a higher forward voltage at the same current mean the LED is using more ...
0
votes
0answers
28 views

Interpreting LED output distribution specification

I have specifications for an LED which gives the following graph of spacial output distribution. I am not sure how to interpret this. As I see it, it could be one of two ways. To make ...
0
votes
0answers
15 views

Candles: paraffin and flameless, which is the most environmentally friendly?

How could one compute (at least the scale of order) the well-to-flame energetic cost of a paraffin wax candle burning one hour (including CO2 and CO)? Can it be compared with a flameless candle (LED ...
0
votes
0answers
87 views

In which direction along a GaN (wurtzite) crystal are only Ga atoms being observed?

So, if you have an electron microscope image of a GaN crystal, and that it shows only white dots which represent Ga atoms. No nitrogen atoms are seen in the image. Along which direction is this ...
0
votes
0answers
106 views

How far away are we from a UV LED operating at around 100nm?

So far, we are down to around 250nm for UV LEDs. If I could get one at around 100nm that would ionize air I would find it very useful. Any ideas on whether this wavelength is feasible for a LED?