Questions tagged [light-emitting-diodes]

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2answers
11 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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0answers
17 views

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
48 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
80 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
42 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
56 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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14 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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17 views

(Color Temperature) How to calculate combined color temperature (kelvin) of two different sources

I have been looking for a while but I can't seem to find any information on this. I would like to figure out the formula to calculate the CCT of two calibrated sources of light relative to their ...
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1answer
43 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
46 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
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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
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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
96 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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1answer
48 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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2answers
89 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
37 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
118 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
22 views

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
56 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
44 views

Need of LED Modulation

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
55 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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0answers
17 views

Link between a LED or laser efficiencies and carrier mobilities

Does anyone know if there is a simple formula/relationship between an LED or laser power conversion efficiencies (PCE) and the carrier mobility. So given everything the same, if I change the ...
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1answer
62 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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1answer
296 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
85 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 ...
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2answers
187 views

Alignment of Michelson interferometer using IR LED

I am trying to align the Michelson interferometer using 780 nm LED. But I am not getting any interference pattern in the CCD. Initially I align the interferometer using Laser to get the equal path ...
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2answers
434 views

Focusing white LED light into a spot as small as possible

An aperture (about 1mm) is placed 2cm in fount of the LED, collimated by a f=50mm lens, then focused by a f=100mm lens into a 3x3mm spot. The focal distance of the second lens cannot be decreased. ...
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1answer
33 views

reverse / dark / leakage current

what is the difference between reverse, dark and leakage current of a (photo-)diode? From my current understanding it all seems to be the same?
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20 views

SiO2 layer in diodes

Can somebody please explain the purpose of this SiO2-layer? Thank you!
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1answer
21 views

Can a controlled lighting environment be a substitute for bandpass light filters?

Could illuminating a subject with different LEDs be used instead of bandpass filters? I am experimenting with capturing surface reflectance using a monochrome camera. The traditional approach to ...
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1answer
60 views

What wavelength of light has the greatest rate of reflection off of ice?

We are using a camera that is nearly flush against frosted ice (not perfectly clear, but pretty close). We are currently using white LED's, but very little of the light gets reflected back into the ...
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54 views

What causes observed color differences in white LED's for near and far fields?

While running towards traffic early morning before sunrise I recently noticed that the new automobile LED (white) lights when viewed at a distance appear blueish, but when the light is viewed much ...
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0answers
51 views

Intuitive explanation: how does a LED work?

I'm looking for an intuitive explanation of how a LED works. I have a bachelor level understanding of math (I did take some physics courses as well, but nothing too advanced). I'll explain what I know ...
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1answer
451 views

Why do parallel LEDs glow brighter when one is replaced with an incandescent bulb?

I have a chandelier with 10 LED lights in parallel. I replaced one with an incandescent lamp and now the 9 LEDs glow much brighter. Why does happen?
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1answer
105 views

Converting illumination to irradiance

I need get intensity of an LED light source, but I cannot convert lux to $W/M^2$ How does one convert illumination to irradiance? And what is the irradiance formula?
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2answers
2k views

How is it I can see the infrared Face ID on my iPhone X? [closed]

I’ve tried using Face ID in the dark on my new iPhone X and I can very clearly see the infrared flood Illuminator light up as well as the infrared dot projector. Is it possible for humans to see ...
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1answer
43 views

Why does the light from high-power LED source look bigger in the image plane?

Maybe my question is not clear enough so I will post a picture I found for simplicity: https://upload.wikimedia.org/wikipedia/commons/8/8d/Ronja_beam_Prostejov.jpg In the document it is explained ...
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2answers
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Bike light: what consumes more current, continuously on or blinking?

I've been riding my bike many nights wondering the following question: What consumes my LED bike-light battery: the continuously on setup or the blinking setup? It might seem trivial, since the ...
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6answers
369 views

Why does the LED turn off if the high current is going through the short?

None of the other questions related to short circuits seems to answer my question. I understand how short circuits work theoretically, that if there is a path with no resistance in a circuit then all ...
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0answers
259 views

Why is a white LED color spectrum more continuous than CFL spectra?

As far as I understand, white LEDs and CFLs both use phosphor mixtures to convert part of their primary emission spectrum to longer wavelengths. What puzzles me is the difference in the resulting ...
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1answer
319 views

Ruby fluorescence activation spectra

You might have seen the absorption spectrum of ruby: it has distinct absorption peaks near 400nm and 550nm. Looking at its absorption graph, one could expect some fluorescence when excited from a ~...
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1answer
30 views

Noise produced by foam illuminated by a pwm led

I have a led headlight which seems to use pwm modulation to ajust brightness (led lenser xeo 19R). With an intermediate light power (i.e. not 0% or 100%), the light produce a really small noise, which ...
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2answers
749 views

What is the mechanism behind the halo around LED lights?

Was at a musical event last night, outdoors in what might be called a "beer garden", and I noticed that many of the lights in the area were surrounded by a sort of "aura". The more distant lights (...
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1answer
443 views

Focusing LED using a Fresnel lens at different distances

Simple setup: A Red LED in front of a small fresnel loupe/lens (credit card size). Using a screw I can adjust the distance between the LED and the lens. The LED is centered with regard to the lens. ...
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0answers
37 views

Object that is visible only at certain light intensity

I have a lux meter, by which we can measure light intensity. We have one box, in which we inject the light from a hole. What we want is, if light intensity for e.g. Lux value is between 400 to 450 ...
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1answer
70 views

Why does the spectrum of blue LEDs appear to have two peaks?

Due to having poor distance vision and thus strong corrective lenses, I'm "blessed" with the ability to see the spectrum of a light source whenever I look at it from an angle. One thing I've ...
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2answers
151 views

Does the lumen value of a light bulb take into account the inverse square law and volume of a room?

For example, I am trying to calculate the number of 800lm light bulbs required to light a 16sq meter bed room with a 2.5m celling that doubles as a study. Assuming 75 lux is required, this converts to ...
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1answer
108 views

If the energy of photons at the bottom of the visible spectrum (~720 nm) is 1.72 eV, why does a red LED light up at only 1.48 V?

I have a red LED (623 nm peak wavelength) which I am able to light up at 1.48 V. I thought the switch-on voltage should be determined by $hc/(e\lambda)$, but that would give 1.99 V for 623 nm. Even ...
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2answers
626 views

What does the spikes and curves in the spectral graph for compact fluorescent lights represent?

I have read from sources that the curves are generated by the phosphors in the bulb, and the spikes are caused by the mercury vapor. However, if the mercury vapor's release of uv particles combine ...