Questions tagged [light-emitting-diodes]

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12 views

Understand how diffusion film for LED lighting work

I'm reading the datasheet of a Diffusion film for LED lighting: Kimoto OptSaver L-series. As far as I understand here the "Total light transmittance" parameter states how much of the ...
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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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Using an LED for Doppler cooling

Would it be possible to use an LED to perform Doppler cooling? I understand that the linewidth of lasers is around a tenth of LEDs. I feel that there should be a trivial reason that should explain the ...
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34 views

Monochromaticity of laser [closed]

I am writing a paper on doppler cooling for the course of a laser in college. Doppler cooling is basically an application of the highly monochromatic nature of lasers (right?). I understand that the ...
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1answer
36 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 ...
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2answers
45 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 ...
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69 views

Spatial intensity distribution of a LED source

I hardly find instruments for applications like wavefront sensing of large optics (more than 200 mm diameter) using a LED source or halogen lamp. Is the maximum width limited by the low spatial ...
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25 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 ...
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28 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{...
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123 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 ...
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1answer
92 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 ...
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Collimating 3 LED light sources into one point

I am creating a bespoke piece of lighting which requires modifying an existing piece of equipment Currently the equipment is lit up by a single SMD white led chip, however I am going to be replacing ...
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1answer
125 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 ...
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1answer
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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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Is the current in reverse biased PN junction due to drift or diffusion?

Wikipedia says :https://en.m.wikipedia.org/wiki/Saturation_current The saturation current (or scale current), more accurately the reverse saturation current, is that part of the reverse current in a ...
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1answer
32 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 ...
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53 views

How to design a collimated (no hot-spot) RGB light source?

I'm an electrical engineer tinkering with a tiny display that has an LED back light. It looks like a little square and it quickly cycles through red, green, blue light to produce the final display. I ...
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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 ...
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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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2answers
31 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 ...
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21 views

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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39 views

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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53 views

Shockley diode equation - temperature influence

when looking at Shockleys 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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1answer
51 views

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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2answers
65 views

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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1answer
130 views

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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51 views

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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1answer
19 views

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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20 views

How to calculate lux value?

I tried calculating lux value for my LED by using the formula the (luminous flux / area), i obtained viewing angle and luminous flux value from LED datasheet, then with the angle i calculated the area ...
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16 views

How can I calculate the UV LED dose having few parameters such as wavelength and output power of LED?

i have UVC led with 270nm wavelength and output power of 70mW. The total length of the passage for the de-contamination is 40cm and the total time is 60 seconds. Is it possible to calculate the UV ...
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1answer
107 views

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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32 views

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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1answer
59 views

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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114 views

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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302 views

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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36 views

Semiconductor structure confinement modes

Today, I would like to simulate the field intensity in an emitting structure such as a laser diode. With this field, I will be able to calculate the confinement factor of my device. I put an ...
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1answer
24 views

Reverse biased semiconductor diode: Name of the current due to which the depletion layer is getting widened?

I know, that in a reversed biased connection the reverse saturation current flowing is negligible but before the depletion layer is widened to its maximum capacity. It seems the current flowing ...
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37 views

How much R and B spectrum changes over time for LED?

I am trying to see if there is any data on the R and B spectrum change over time for a LED. For example after 5000 hrs of operation, there are few light which gets dull, which is mostly that the ...
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3answers
805 views

Is there any relation between turn on voltage of LED and the colour emitted?

It is evident from the above V-I graph that longer the wavelength of the light emitted lower is the turn on voltage. I know that turn on voltage is voltage required to have significant current that ...
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1answer
101 views

Can white light have two spectral peaks?

I was looking at a graph on the receptive ranges of the 3 types of color sensitive photoreceptors in us humans, and I had the idea that if we place only two peaks at the right places, we'll be able to ...
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2answers
397 views

Is it possible to use fresnel lens(es) to focus an LED light on a headlamp

I was hoping that someone would be willing to offer any insight or guidance they have on a project that I am working on. We are trying to use a lens mounted on a headlamp to focus a plain white light ...
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1answer
862 views

LED heat radiation

Consider two bodies in space exchanging heat solely by radiation. Let's call them a star and a planet. If the star contains a heat source and the planet doesn't, it can be shown that temperature of ...
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39 views

Calculate irradiation from a LED lamp

I am working with cell culture and I want to irradiate a 96-well plate with a single color led lamp (let's say the peak is at 450nm). It's just a test, so a rough estimation would do. I've been ...
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2answers
138 views

Opposing Laser Beams Turns One Laser Off

When I send two separate laser beams directly into each other one of the beams goes completely out. These are inexpensive 5mv red diode lasers. What’s happening inside the laser to make it “turn off”? ...
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1answer
52 views

LED flicker vs human perception

I have read this question: https://mechanics.stackexchange.com/questions/43070/why-do-the-headlights-of-supercars-looking-flashing-on-video where cdunn says: So when you slow it down, you're ...
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911 views

Light reflecting off rain from bike light

The other day when I was cycling back from work in the rain I noticed an effect from the light on my bike. A single raindrop, as it passed the light, appeared as multiple dots or dashed that followed ...
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187 views

Viewing LEDs at great distance

Say I put a satellite in orbit with several LEDs on the outside: red, yellow, blue, white and green. Could I see them from the ground with consumer-grade binoculars or telescopes? If I can see them, ...
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Amateur student making a demo of electromagnetic induction via copper coil and magnet

I'm trying to observe electromagnetic induction by creating a copper coil solded to a diode led and waving an alnico magnet inside the copper coil's core. You can see my amateur setting below (...

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