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2
votes
1answer
27 views

How does infrared light behave through water?

I have a project involving the detection of the presence of water in a cylindrical transparent plastic container (diameter=25cm) And I cannot put any device inside, so I was thinking of using and IR ...
1
vote
1answer
49 views

Are RGB LED's only capable of producing three colors of light? What about all the other colors?

I had a light sensor hooked up to an LED and noticed that it only read a constant lux value when I had any of the RGB values at 255. Anything less made the lux value fluctuate quite rapidly. I get ...
0
votes
1answer
51 views

What happens when an AC source is connected to a capacitor and a LED?

When a DC source is connected to a capacitor and a LED, and the voltage is removed when capacitor is charged, the capacitor supplies current to it for some time. What happens if this DC source is ...
0
votes
0answers
19 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 ...
20
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 ...
0
votes
0answers
38 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 ...
-1
votes
2answers
48 views

Why is LED important in communication? [closed]

How does LED transfer data and how is it used in Communication? How does different colors of LEDs contribute, blue LEDs especially?
0
votes
0answers
33 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 ...
2
votes
0answers
43 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 ...
1
vote
0answers
33 views

Superluminescent LED [closed]

How do Superluminescent LED generate amplified spontaneous emission? Moreover," a superluminescent LED combines the spatial coherence of a laser diode and the temporal incoherence of an LED. " Please ...
0
votes
1answer
99 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
2answers
52 views

Why photoluminescene spectrum is not identical to electroluminescence spectrum?

Electroluminescence (EL) and photoluminescence (PL) spectra are not identical: there's a small red-shift of the PL spectrum relative to the EL spectrum. Why is this happening if both EL and PL are ...
0
votes
0answers
30 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 ...
1
vote
0answers
14 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 ...
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 ...
2
votes
1answer
72 views

Why does this illumination pattern of an LED light going through a small pinhole not emulate the point spread function?

I have an optical setup where a component LED passes through a 50 um pinhole, and creates an illumination pattern on an image sensor approximately 5 cm away that looks like the following: Now, I'm ...
0
votes
0answers
31 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 ...
1
vote
0answers
133 views

Doesn't this LED created by MIT violate the second law of thermodynamics? [duplicate]

Here is the article I am referring to: http://www.wired.co.uk/news/archive/2012-03/09/230-percent-efficient-leds In their own words (or at least the article writer's), "it appears to draw in heat ...
1
vote
0answers
37 views

Can you grow more Biomass in a brickhouse only powered by solar cells than in a greenhouse? Will we ever be able to? [closed]

Right now I read that 1m² of solar cells generates roughly 100Watts of energy. There are really efficient Grow LEDs that use only two spikes in the lightspectrum to make plants grow. I have seen some ...
3
votes
1answer
97 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 ...
1
vote
2answers
139 views

Why doesn't silicon emit light? [closed]

Why doesn't silicon re-emit light when light falls on it? Or if it emits light then why we can't see it?Hence it has valence electrons.
-1
votes
1answer
191 views

What is the underlying physics that makes Li-Fi “100 times faster” than Wi-Fi? [closed]

Consider this webpage, which compares how the two work. Particularly it says (and I'm paraphrasing) that Lifi transmits using light from LED bulbs and WiFi uses radio waves. Well, both are EMF waves, ...
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
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
71 views

measuring average directional intensity of LED?

Although I am poor at physics and math I want to compare two light sources of which I haven’t decided the specific brand yet. I was thinking of florescence bulbs versus LED lamps. So something like ...
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 ...
13
votes
2answers
926 views

Why fast eye movement splits a white LED into the RGB components?

I have a "white" LED as the notification light on my phone. When I look at it straight it looks whitish, but when I move my eyes around (or shake my head) I suddenly see glimpses of red and green (and ...
3
votes
2answers
337 views

Can I use fluorescent light bulbs to calculate Planck's constant?

We did an experiment today to calculate Planck's constant, $h$. We measured the knee voltages $V$ of different LEDs (red, green, orange, blue, violet) and plotted them against the frequencies $f$ of ...
2
votes
1answer
251 views

Why did LED lit up while soldering? [closed]

I was soldering an LED when accidentally the soldering wire touched the LED's other Pin while the soldering iron was touching the other and the LED lit up, not bright but bright enough to be seen. I ...
1
vote
0answers
22 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
316 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 ...
2
votes
0answers
58 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
46 views

What causes this pattern in the reflection of a laser on a screen? [duplicate]

When I shine a red laser behind me at a wall I see a strange reflection occurring on my laptop screen Why does this happen? The pattern on my screen occurs exactly where the laser is hitting the wall. ...
2
votes
2answers
117 views

How is the backlight in a LCD monitor dispersed equally?

How is the backlight in a LCD monitor dispersed equally? I mean are there any layers that disperse the light?
0
votes
1answer
47 views

Diodes in AC current

If in AC current, the direction of the current is always changing, then if one was to place a diode (for simplicities sake lets say an LED) in an AC current, would it flash to the frequency of the ...
0
votes
1answer
43 views

Can high-power LEDs remotely control a whole room? [closed]

Let's say I have 4 appliances in rectangular based room of about 60 square meters with white walls. The appliances are using infrared receivers with a filter of 38 kHz. Would it be possible to apply ...
1
vote
1answer
1k 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: ...
3
votes
0answers
269 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 ...
1
vote
2answers
167 views

Do photons emitted from a LED show bunching?

If photons are emitted from a thermal source, we get photon bunching. For coherent radiation, the detection probability doesn't change after detecting a photon. For single photon sources, we get anti-...
3
votes
1answer
305 views

Laser diode spectrum vs LED spectrum, why so much difference in broadness?

I've been reading about how light is produced in both laser diodes (the most common types of lasers) and LED's. The mechanism seems very similar if not exactly the same: one applies a potential ...
1
vote
2answers
187 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 ...
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 ...
4
votes
1answer
848 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 ...
0
votes
0answers
113 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?
3
votes
1answer
2k 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.
4
votes
2answers
156 views

Is there something equivalent to a diode for light?

In electronics a diode is a component allowing current passing in only one direction, and blocking the other side. I'm wondering if something similar exists for visible light or other EM waves, like ...
2
votes
2answers
194 views

Why do we call a white led with high color temperature “cool”?

one can buy LED bulbs with defined color temperature. why cool white = many kelvins (= high temperature?) why warm white = few kelvins (= low temperature?)
9
votes
2answers
156 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 ...
4
votes
2answers
14k views

Does staring at a bright LED light damage your eyes?

According to this article it seems that it is the UV part of the spectrum from the Sun that causes damage to the eye. Would it therefore be "safe" to observe directly an equivalent energy density LED ...