Questions tagged [light-emitting-diodes]

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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 (...
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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 ...
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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 ...
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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 ...
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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 ...
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Why there is no current when diode ia reversed biased?

I try to understand why, really, there is no current (except for leakage) when a diode is reverse-biased. I studied several texts, and noone really explains, like for instance this otherwise very ...
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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 ...
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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'...
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Compute UVC Irradiance On A Surface

I would like to be able to get a ballpark approximation of the Irradiance on a surface at a distance away from a UV source. The datasheet gives the following: Radiant Power Lambertian Emitter Graph ...
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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-...
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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.
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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 ...
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Will a reflective surface inside a lit tube increase luminosity disproportionately more than heat?

Okay, so I have a long tube, shaped like an irregular octagon across its Cross section (wider than tall), with vertical slats running along the length of the tube (like in this picture) The tube is ...
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Why do we need an emissive layer in OLED?

Currently, I am studying the working Principle of the OLED screen panels. I have this question: why do we use the emissive layer in between the Electron & Hole transfer layers in OLED devices? Why ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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{...
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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 ...
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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 ...
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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 ...
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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)/...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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Relationship between Optical Power output and luminous intensity

I have an LED with the following specification which I'm using for oxygen saturation measurements. Here the optical output power is given as >1.2mW for RED LED and >0.5mW for IR LED. How to ...
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Cut-off frequency of an LED [closed]

I'm trying to solve this problem: A GaAs LED is at $ 300 K $ when the current density is 100 $A/cm^2$ . The width of the active region is $ 1 µm $. Assume that, for that current, we are in the strong ...
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Shockley diode equation - temperature influence

when looking at Shockley's ideal diode equation I wonder what "meaning" the temperature has in there? If I assume $$I(T) = I_0 \left[\exp \left( \frac{U}{k_BT/q}\right)-1 \right]$$ and vary ...
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How do LED screens emit light?

How does an LED television screen emit light? My understanding is that the screen consists of many pixels, and each pixel has red, green, and blue LEDs. An electrical current runs through every red, ...
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How do wavelengths add-up?

If I have 3 LED lights of following colors and wavengths: Red 650 nm Blue 450 nm Green 550 nm All three are placed side by side and turned ON.. then what will be the wavelength of the combined light ...
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How can I find the external quantum efficiency of an LED?

I have a setup where I can measure the optical power, in watts, the current, the voltage and the spectrum of an LED. Is it possible from this to calculate the external quantum efficiency? I realise I ...
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Model radiated power from an LED

For a range of LEDs I'd like to model their performance and predict the flux density across an area using manufacturers datasheets. Eventually I'd like to take various power measurements and calculate ...
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In a LED the electrons from the n-type combine with the p-type which creates a photon. Are the electrons 'lost' or gone when this process takes place?

In a LED the electrons in the n-type move to the p-type where they are then 'combined' with the holes in the valence shell of the p-type which produces photons. My question is that when this happens ...
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Is an LED's voltage response to current non-linear with temperature?

I have been measuring the voltage response to current of an LED. It's a point source LED with an oval emission area of 40x150um (link to datasheet https://www.daido.co.jp/en/products/point_source_led/...
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How would you make a RGB LED equally bright to a broad-spectrum white LED?

Say you had a broad spectrum white LED (all visible wavelengths) and you wanted to make a RGB LED (just red-green-blue wavelengths) that could produce white light of equal brightness to the broad-spec ...
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Infrared light beam diffusion

I have a closed box with a hole in the wall. A IR beam is directed at the front of the box. Due to a small 6mm borehole in the wall only a certain part of the beam can pass trough. The left small ...
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Characteristic functions of a non-ohmic material

We know that Ohm's laws are experimental laws. Ohm's first law for ohmic materials follows a linear approximate progression of the kind: $$\frac{\Delta V}{I}=R$$ What are the functions of type $$\...
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Would a perfectly collimated laser beam have a flat intensity distribution?

I'm trying to simulate a collimated laser beam in some FORTRAN and am wondering about the intensity distribution of a perfectly collimated beam: would it be a flat distribution (equal intensity across ...
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Why are blue light-emitting diodes important enough to warrant a Nobel prize? [closed]

I am using a miniature blue light as night bed room light since my childhood. For me blue light-emitting diodes almost look like miniature blue lights. I don't see any fundamental scientific ...

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