Questions tagged [light-emitting-diodes]

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7 views

How can i control and monitor the UV-C LED irradiation? [closed]

I have to construct a UV-C LED and i have to make sure to control the radiation dose and monitor it. How can i make it happen?
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2answers
53 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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3answers
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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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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
22 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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36 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
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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
57 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
60 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
761 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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0answers
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
117 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
45 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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895 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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2answers
52 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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1answer
51 views

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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1answer
48 views

LED flashlight Lens / Reflector Choice for Collimation (Large throw)

I am trying to build a LED flashlight with a large throw (beam of light should reach very far, be as parallel as possible). I am using a led with approx 84watt (10x10 COB, 100Watt rated) which should ...
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1answer
54 views

Diode Diffusion Capacitance

I'm confused on the topic of diffusion capacitance in a diode. In the book, Solid State Devices by Streetman and Banerjee, I see an equation for the diffusion capacitance which gives an exponential ...
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14 views

Calculating mix ratio of primaries for given chromacity

I'm trying to calculate the intensities of a Red, Green and Blue, such that they mix into a (white) color. I'm given the wavelengths of the three LED's and their luminous intensity for a given drive ...
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1answer
205 views

Finding the Injection Efficiency and IV Characteristics of an LED

I have taken IV measurements for several LEDs and now need to calculate their injection efficiencies. I understand that the injection efficiency: $\eta_{pn} = I_{D}/I$ Where $I$ is the total ...
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1answer
68 views

Calculate Retinal irradiance (W/cm² to log photons/cm²/s)

I have been trying to calculate what retinal irradiance value I get with a 1 blue LED system. Since the manufacturer didn´t give the spectral distribution information, I will approximate LED as a ...
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123 views

Why is silicon absorbing visible light?

Here it is shown that silicon absorbs visible light: but the band gap energy for direct transitions is 3.6 eV which does not match to this absorption coefficient. Instead, the band gap energy for an ...
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31 views

How many photons will a scintillation crystal emit?

The question is already in the title: How many photons will an excited scintillator emit? It is probably mainly given by the energy of the impinging particle and the bandgap energy. But also probably ...
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Optimal paint for UV fluorescence?

If we assume that a light source with 365 nm is the optimal source for how strongly we perceive UV light when it hits a UV fluorescent surface, what would be the optimal colour to paint such a surface ...
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1answer
44 views

Change the color of a LED Display (Make it appear different)

I want to know if it is possible to make a red L.E.D. display appear a different color, at least theoretically, but ultimately for a D.I.Y project. Based on answers to this question (How do color ...
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2answers
22 views

Optics - Polarization's Effect in a Blazed Reflective Diffraction Grating

I'm doing an undergraduate research project, part of which requires me to build an extended cavity diode laser (ECDL). The new diode mounts take receive the diode in a 90 degree rotation of the old ...
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Is activation voltage the sum of voltage required to collapse depletion layer and band gap energy?

Is the energy released when an electron moves from the valence to conductance band states the activation voltage or is activation voltage the energy required for electrons to overcome the depletion ...
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1answer
56 views

How do electrons exit LEDs? Aren't they in the valence energy state?

If a conducting electron reduces to the valence band in an LED, where does it get the energy to go back to the conductance band upon leaving the diode so current can flow? I'm confused as to how ...
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2answers
236 views

Why is my measured LED activation voltage lower than theoretical?

I have done an experiment to measure Planck's constant. I measured the activation voltage of the LED for each wavelength used. I calculated theoretical activation voltage results using the energy of ...
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1answer
45 views

What is the simplest way to get the light of 50 visible LEDs into a multimode glass fiber?

LEDs are cheap. How can I get all their light into a fiber? Even if it is only 1% from each LED, it would be useful. Any proposal is welcome. I read about fiber combiners, but they are not helpful. I ...
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1answer
76 views

Would 2 people wearing identical night vision goggles be able to see each other from afar? [closed]

From what I understand, this is how night vision goggles (NVGs) function: The environment is illuminated by forward facing IR LEDs. A portion of the light bouncing off of the scene passes through an ...
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21 views

What is the fastest way to photodissociate/bleach melanin - with lasers or LEDs - without heat?

Melanin is the chemical that makes our skin dark. Melanin absorbs in very well in the UV, but when one does so, the solution/molecule gets very hot. Is there a way to photodissociate melanin without ...
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1answer
60 views

Can RGB screen color exist in real physical world?

For example the bright royal blue color; R0 G10 B220, HEX: #000ae1. I know this color cannot be printed nor painted. But can this blue color exist in the real world other than on a digital screen? For ...
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1answer
124 views

Is the spatial coherence of light a requirement for creating a well-collimated light beam?

I was wondering if, for creating a well collimated light beam, the spatial coherence play a role. In particular, I understand that a laser beam can be well-collimated with respect to light coming from ...
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2answers
573 views

Why does the p-region have a higher energy level than the n-region in a diode?

Looking at the image below, I'm curious as to why the p-type region is at a higher energy level than the n-type region when no external voltage is applied. How is that? The E-field, if I'm not ...
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1answer
42 views

Depletion layer of solar cell? [closed]

What happens to depletion layer of solar cells when light is falling on it? Please reply as soon as possible. Thank you
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2answers
332 views

Difference between diode and LED

What is the difference between a diode and a led? I know a led is a diode and I know how they are used and so on but I'm not really sure why a regular is not also light emitting. Therefore, what is ...
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60 views

Breadboard LED circuit

Please, just a quick question, am I right that the reason why LED is not lighting is: LED is connected parallel to the wire The wire has much lower resistance, so nearly all current is flowing ...
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3answers
255 views

Why can blue LEDs be used for generating white light, but red LEDs cannot

LEDs consist of pn-junctions, so why can blue LEDs be used for generating white light, but red LEDs cannot
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1answer
42 views

Missing link re: how does kelvin relate to temperature when talking about color temperature?

I am an electrician at a commercial electrical company. There is an in-house training program that posits the datum that when talking about the designations of color temperature for lights (for ...
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3answers
237 views

Difference in spectrum of green laser and green LED

In an experiment I conducted I used a spectrometer to find the spectrum of green laser and green led. this is what I found: LED spectrum: Laser spectrum: why is the spectral width of the LED is ...
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0answers
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Calculating required amount of lumen for camera sensor satuation

I am stuck on this problem at work - I hope some of you can help me further. I work with underwater vision and am trying to find way or methodology to get a somewhat estimate of the required light ...
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4answers
206 views

With the same power output, which color of light give the most intensity?

Imagine we have a power source produce constants power in Watt. If I placed blue LED, then red LED, which color gives more intensity and wht color gives the most?
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2answers
82 views

Need of LED Modulation [closed]

I have an experiment of calculating the velocity of light by using phase difference produced (link of the experiment is at the end). The experiment has a control unit which has an LED installed to ...
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2answers
80 views

Is this possible to focus common light (not laser) to a small point in the wall and control it with mirrors?

I want to make something like a laser projector for an experiment but with common light. My question is: is this possible to focus a small point of common light to the wall and control it with ...
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1answer
47 views

Colour Temperature and the thermal temperature [duplicate]

I understand that Colour Temperature correlates with the object's thermal temperature, such as a red-hot piece of iron being ~360c and the incandescent bulb filament is about 2500c. Why are sources ...
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1answer
91 views

How to evaluate LED illuminance based on luminous flux and directivity / radiation pattern?

I am building an LED-light and am trying to figure out how many LEDs I need to be on it. I know how much illuminance I need as well as the distance to the subject and the luminous flux of one of the ...
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2answers
590 views

How to find out the wavelength for the blue led diode?

I need your help as I am stuck and I dont know where to start. I have got four blue leds diode that come with dark blue led lights that I really want to get the same led colours for my 3 fans, but I ...
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1answer
367 views

Diffusing a laser?

I haven't been able to find much information about this, maybe I'm searching the wrong thing but, how would you diffuse a laser beam from a thing collimated beam, into a "cone" of light? More ...