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Questions tagged [light-emitting-diodes]

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Does the coherence of light sources make a difference in exciting fluorescence?

Using LED vs laser as light sources in wide-field epi-fluorescence microscopy are both popular choices. It seems that high intensity single color LEDs (such as this one) emits high radiometric power ...
Jason M's user avatar
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Why is the energy lost by an electron in passing though the LED = energy of the emitted photon?

I understand that the energy of the emitted photon = energy between the conduction band and valence band, but why does the work done by pushing the electron through the depletion region equal the ...
Maxine's user avatar
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Forward voltage of LEDs from quantum mechanics perspective

I have a very elementary understanding of LEDs and semiconductors altogether, but a more solid understanding of QM, and I was wondering if there was a way to explain (preferably mathematically) ...
JBatswani's user avatar
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How to align a Mach-Zehnder at 810 nm?

I have a task to arrange MZI using very weak source with photons coming one at a time. On top the wavelength is 810 nm. How to 'see' the interference pattern to 100% in one channel and 0% in other. I ...
Mercury's user avatar
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1 answer
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Can two laser diodes of the same type and wavelength, be synchronized to emit light in the same phase, while working in a CW mode.?

Can two laser diodes of the same type, power and wavelength, be synchronized to emit light with lightwaves in the same phase, while working in a continuous wave mode (CW) ?
Jimski's user avatar
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After 20 years, do we now understand more why the nobel prize discovery blue LED GaN works?

From the book The Blue Laser Diode: The Complete Story, it said that Indeed, maybe one of the most puzzling and amazing facts about present gallium nitride-based devices is why they work so well at ...
Tong Su's user avatar
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2 votes
2 answers
397 views

LED Lambertian law and irradiance

I have a irradiance reading from an LED which does not seem to make sense. I was hoping someone could shed alittle light on the issue. The LED is question has a relative radiant intensity which ...
mpcengineer's user avatar
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284 views

Calculate Radiant Intensity from Radiant Power and estimated Radiant Distrubution of infrared LED [closed]

Consider the infrared led TSAL7600 which has the following properties: $$ \Phi = 35 mW $$ $$ I_e = 25 mW/sr $$ The half angle is $30^\circ$ and: $$ I_r(\theta) = cos^{4.818}(\theta) $$ is a good ...
InTheWorks's user avatar
1 vote
3 answers
389 views

What specific properties of laser light make it dangerous?

What makes a laser more dangerous than a high powered single color LED for example? Is it the fact that it's coherent light, all the photons have the same wavelength, that it can be focused to a small ...
Plasmabot's user avatar
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Chaotic monochromatic light

I am currently reading through the book "The Quantum Theory of Light", by Rodney Loudon, in order to prepare for a science fair project which will involve measuring plant response to ...
slithy_tove's user avatar
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1 answer
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LED forward or reverse bias

Are LEDs connected in forward bias or reverse bias? A recent question I got wrong said that LEDs are connected in reverse bias, but a general Google search tells me LEDs connected in forward bias ...
kenntnisse's user avatar
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1 answer
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How does 3cm microwave pass through a 0.5 cm grating?

This YouTube video prompted a question. If the wavelength of the PASCO microwave generator is about 3 cm, how do we explain that a significant portion passes through a 1/2 $cm^2$ screen? I have a ...
daniel's user avatar
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Can an LED emit photons with energy (in $\rm eV$) larger than the voltage drop across it (in $\rm V$)?

I recently had a discussion with someone who told me that they have a UVC (260 nm - 270 nm) LED with a forward voltage of 3.3 V. I told them that this must be impossible, because an electron dropping ...
MaxParadiz's user avatar
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2 answers
31 views

Does carriers lifetime introduce any dispersion to a LED diode emitter?

I'm asked to calculate the maximum chromatic dispersion coefficient D for which an optical cable is able to transmit at a 100 Mbps bitrate working in SMS. The maximum bitrate is given by B≤1/2∆τ, ...
Ketterle's user avatar
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41 views

Would an ideal, p-n based LED, ever stop producing light if it had a finite amount of doping?

I'm trying to understand how long would an LED last if there were no manufacturing/wear and tear imperfections in the product, just by exhaustion of the material that allows the transduction of ...
A. Fenzry's user avatar
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2 answers
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Does a diode show an "effective resistance" in a circuit, and how does that affect current drawn?

I was taking some measurements on a simple circuit consisting of a 3.7 volt battery (an old one used for vaping and such), a 20mA LED that has a listed voltage of around 2.3 V, and a resistor of about ...
Jesse's user avatar
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Will a circuit be closed if we make a 100% efficient LED?

Suppose we make a LED that is 100% efficient, that is, it converts 100% of electric current we supply to light. Based on my understanding of electric current, as there is no current flowing back to ...
currentphysics's user avatar
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1 answer
2k views

Determining ideality factor of diodes from IV curves

I'm currently doing a semiconductors lab and one of the tasks is to examine the IV characteristics of diodes to determine the values of the ideality factor, $n_{id}$, and the reverse bias saturation ...
probablysid's user avatar
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185 views

How to calculate luminance, given a light source's luminous intensity?

For example, let's suppose I have $2.5$ mm diameter LED with a diffuse lens; it has luminous intensity of $2.0$ cd. Let's say it has viewing angle of 120 degrees and I'm viewing it head on. How would ...
Azmisov's user avatar
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3D Display Technology Technique

I was randomly reminded of 3D TVs/Nintendo 3DS and was wondering about how they work without glasses as I was already familiar with 3D with glasses. Everything I found online seemed to be about using ...
Karric's user avatar
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1 answer
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Why do efficient blue emitters (LEDs,OLEDs, quantum dots) take much longer to discover than red and green emitters?

For example, it took over 3 decades to create efficient blue LEDs in the lab after the red and green leds were discovered. For OLED displays as well, the red and green pixels are phosphorescent oleds ...
Aqua Neon's user avatar
2 votes
2 answers
296 views

Why does total internal reflection (TIR) drastically reduces the efficiency of LED?

Total internal reflection (TIR) is the primary reason of efficiency loss in LED bulbs. LED chips are made of GaN, which has a much higher refractive index than surrounding materials. Because photons ...
哲煜黄's user avatar
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Searchlight Simple Optics Problem

Here is my problem. I want to make a working model of a searchlight. I can't sensibly make a parabolic reflector at this scale so I planned to place a small 0201 LED (0.6 x 0.4mm) in the body of the ...
ModelMan's user avatar
1 vote
2 answers
79 views

Pumping Nd:YAG laser with LEDs... would it work ? What would be the efficiency?

I find on Wikipedia that Nd:YAG absorbs mostly in the bands between 730–760 nm and 790–820 nm, and are pumped with flash tube or laser diodes. Couldn't it get pumped with normal near IR power LEDs (...
Camion's user avatar
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0 answers
51 views

Why some line lasers of power less than $\rm 1mW$ is brighter than that rated for higher power?

I want make a line laser that uses 1mW power and should be visible at a distance of 10 m. I have a locally available laser module of 5mW which barely reaches 5 meters whereas Bosch GLL5-50X claims to ...
dharmikP's user avatar
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Clarifications about units of Photon Flux (PF) and Photon Flux Density (PFD)

I have an emitting source of light (this LED - Light Emitting Diode, UO variant). On page 5 I read the minimum PF Photon Flux is ...
Mark's user avatar
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1 vote
2 answers
744 views

Are laser diffuse reflections really so dangerous?

Class IV lasers are lasers with an optical power higher than 500mW, and for these lasers "even diffuse reflections can cause permanent eye damage". Well, I would like to understand how this ...
RandomGuy's user avatar
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1 vote
1 answer
1k views

Convert $\rm Lux$ to $\rm W/m^2$

I use four LED matrix (UV, green, red, blue) to irradiate a solar panel with an area of S at a distance. The matrix is located at a distance l from the solar panel. I want to plot the volt-ampere ...
Сергей Корягин's user avatar
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2 answers
1k views

Blinking LED and the human eye/perception

When an LED is flashing at 2 times a second, the human eye can perceive the ON and OFF state. We can clearly see when the ON state is and when the OFF state is. When it is flashing 10,000 times per ...
Mars Sojourner's user avatar
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1 answer
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Could a large panel of LEDs be used for station keeping in earth orbit?

Hall effect and other ion thrusters require propellant to operate and thus have a limited usable lifespan in orbit. In typical operational use, the force they produce is in the 25mN - 250mN range. It'...
Georges's user avatar
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4 votes
1 answer
2k views

Why don't we have x-ray emitting LEDs?

I've just learnt about how X-rays are produced in existing systems. We barrage a hunk of metal with a beam of electrons, in order to get an effective yield of 20% of the energy converted into useful X-...
Andrew Micallef's user avatar
1 vote
0 answers
39 views

What is meant by "Temperature response of a Light Emitting Diode"?

I'd like someone to clear up the meaning of 'Temperature response' in the context of Light Emitting Diodes(LEDs) because I think I'm confusing it and 'effect of temperature' on LEDs.
Leon Denis's user avatar
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34 views

Light with uniform spectograph?

I've been looking for lights, namely LEDs as they seem to be a more controlled and reliable method of producing light (at least from my degree of familiarity), that can produce light at a very ...
Iter's user avatar
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0 votes
1 answer
91 views

Why do inorganic lasers not experience problems due to triplet loss?

A major problem for building organic lasers (especially if aiming for electrical pumping) is the creation of triplets that cannot classically photoluminesce (forbidden transition) and can interact ...
siete's user avatar
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0 votes
2 answers
127 views

Is high temperature a necessary condition for an object to be a blackbody?

A Light Emitting Diode (LED) is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor recombine with holes, releasing energy in the form of ...
Sasikuttan's user avatar
3 votes
2 answers
1k views

Why is it possible to couple multiple wavelengths into a single mode optical fiber?

I'm quite new to the mode theory, but as I understand, single mode fiber should only allow a single pattern of wavelength + polarization. I'm assuming a non-modulated non-coherent light (a white LED, ...
eyeballpaul's user avatar
3 votes
2 answers
260 views

In LED's do the number of charge carriers (electrons and holes) decrease with time?

According to page-1268-69 of Halliday, Walker & Resnick's Fundamentals of Physics (10th edition), To emit enough light to be useful as an LED, the material must have a suitably large number of ...
tryingtobeastoic's user avatar
0 votes
1 answer
53 views

Working of a lightboard or glass board?

While watching an YouTube tutorial in which the tutor was teaching on some sort of glass board from the behind of this board or which is called as "Lightboard" also, I wondered to know how ...
Ganit's user avatar
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0 votes
2 answers
248 views

How does the difference between electron flow and conventional flow NOT make a difference?

I keep hearing that it doesn't matter whether we use electron flow or conventional flow for direction of current for simple circuits like those taught in introductory electrical circuitry classes. And ...
Doobius's user avatar
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0 answers
191 views

How do photodiode sensors respond to a spectrum of light frequencies/wavelength?

I wanted to clarify about photodiodes used as sensors and about the response, which is given in the form of A/W: What I want to ask about is what kind of response photodiodes normally give with a ...
Tom's user avatar
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0 answers
42 views

Luminance relation between LEDs when connected in series

I am reviewing a homework problem where we are given three LEDs; in the blue ($450$ nm), in the green ($550$ nm) and in the red ($650$ nm). We are told that the current efficiency $$\eta=\frac{...
Jim Β's user avatar
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3 votes
2 answers
988 views

Why LED light changes color when dips into liquid nitrogen?

Setup is simple we jsut need an LED, a battery as source of power, wires for to complete the circuit and a cup of liquid nitrogen and of course gloves and goggles. When the lit led is submerged into ...
user6760's user avatar
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1 vote
1 answer
323 views

Current-voltage characteristics of silicon carbide luminescence

I am currently studying the textbook Light-Emitting Diodes (3rd Edition) by E. Fred Schubert. Chapter 1.2 Henry Round's demonstration of the first LED says the following: The mechanism of light ...
The Pointer's user avatar
1 vote
1 answer
1k views

Should I be concerned about UV light from my IKEA LED lamp?

I have an LED lamp from IKEA very similar to "JANSJÖ" (see https://www.ikea.com/ca/en/p/jansjoe-led-usb-lamp-black-70291232/). One day, I noticed that white paper illuminated by the lamp ...
Quercus Robur's user avatar
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1 answer
79 views

What does the turn on voltage for LEDs depends on except for the bandgap of the material?

I am trying to find out why my LEDs show a different turn on voltage. The material emitting is the same (therefore same bandgap). The stack I have is ITO/Polyvynilcarbazole (hole injection layer)/...
Clarine's user avatar
3 votes
0 answers
38 views

Lab Construction of LED

If given a semiconductor with known bandgap, how might someone construct an experimental LED within a lab? It seems common to prepare solar cells using FTO glass plates with a paste of semiconductor ...
Tristan Maxson's user avatar
1 vote
1 answer
290 views

Black coloured region of smartphone screens

We have all used backlit screen. Indeed, you must be reading my question in one of them. Everyone of us must have encountered, for multiple times, the texts or the images with regions of hexadecimal ...
SteelCubes's user avatar
9 votes
1 answer
2k views

Where is the energy coming from to light my Christmas tree lights? [closed]

Today my wife gave me a little box of solar-powered Christmas tree lights. She bought them last year 2019 but had forgotten she had them so it was only today (a year later) that I took them out of ...
Richard Hammond's user avatar
1 vote
0 answers
42 views

How to calculate LED light output

I'm trying to assemble an array of LEDs to be configured as a solar simulator. I need to compare this array's output to the solar spectrum as a function of W/m^2/nm. To do this I need to go through ...
Caroline van Bergen's user avatar
1 vote
3 answers
399 views

Spectrophotometer using RGB LED

I understand that an RGB LED produces light in three constrained wavelength ranges and that any color beyond R, G, or B (orange, say) is due to the interaction of the cells in our eyes with the ...
Michael Stachowsky's user avatar

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