# Tag Info

53

Most probably because of short wavelength of your green LED and not as monochromatic green as you might expect (x and y coordinates closer to the center). If you take a look at the CIE 1931 curve and plot your red and green x and y coordinates (listed in the datasheet from serious manufacturers, otherwise assume the pure wavelength on the outer rim or move ...

30

It is a bit hard to see from the picture, but since each LED has six pins, and knowing that it is meant for 12V supply, it is extremely likely that the LEDs might be arranged so that there are three parallel chains of three LEDs in series. The blue LED requires approximately slightly more than 3V voltage drop per LED, and since there is 3 in series, the ...

29

Sounds about right. To get white (6500K) using NTSC (colour TV) phosphors, the relative intensities are G=0.59, R=0.3, B=0.11 - most of the energy is in the green, least in the blue. (slightly differently rounded numbers in Wikipedia ) At equal intensity, blue would appear brightest. The actual numbers will differ here (LEDs not phosphors) but the relative ...

19

Blue LEDs require a higher voltage than red and green. If the panels are designed to work on 12 V, there may not be enough voltage to light the blue LEDs when run on 9 V. The blue LEDs must work for the panels to produce white and violet light.

18

It's even a little worse than winny indicates: Green LEDs are finicky. One result is that green LEDs emit over a broader distribution of wavelengths instead of being a nearly laser-like single wavelength. And when you map that range of greens to the xy colorspace you're not on the spectral locus anymore. So even your yellow-optimized RGB LED may not get ...

17

I do not claim the other answers are wrong, but they miss two important points. One of them that I consider the most relevant. RGB-LEDs are not meant to produce white light. They are meant to reach a certain gamut Wikipedia on gamut, i.e. the colour space that can be displayed by the LED. And they do. If the three channels are driven with an 8-bit ...

16

The resistor is there to limit the current into the input pin. The input likely has a very high DC resistance (more than 1 megohm) so negligible current flows (on the order uA) and a negligible voltage drop is produced (on the order uV or mV). The resistor is likely used to slow the slew rate of the connection (the input pin will have some capacitance, so ...

15

The red led will hog all the current because it might only need 2 volts across it to begin conducting. The green and blue LEDs need a higher voltage but because they are all in parallel the red led dominates. Try measuring their respective volt drops when each operates. It's like putting a 5 volt zener in parallel with a 10 volt zener. The 10 volt zener ...

13

The goal of each capacitor here is to smooth out the power supply of each WS2812B. When you power an array of LEDs, there is a good chance that a transient voltage drop will occur and create a flickering effect on your LED strip and most likely on other LEDs that are currently on. If you were directly powering a LED from the power supply, you wouldn't need a ...

11

Those caps are small bypass capacitors, use to filter or buffer the voltage input to an IC. They are cheap and useful and you will find them as close as possible to any IC on any manufactured pcb anywhere. They should not be ommited without expecting funny operation. The speed that WS2812B are already driven at and the current draw of the leds already cause ...

10

I'm taking a guess about what you are misunderstanding, but here goes... colours are already just different frequency waves. This is true, but the frequencies involved are very very high. $f = \frac{c}{\lambda}$. So for a wavelength of 640 nm (red), you're looking at a frequency of about 470 THz. That's 470 x 1012 Hz. We don't have any technology ...

10

These are "decoupling" or "bypass" capacitors. Their purpose is to stabilize the local supply voltage against fluctuations caused by the interaction of varying current consumption in the circuit with the impedance of the power supply network. "Local" in this case means the supply voltage at each individual LED, which is really an integrated circuit ...

10

I used Firefox Web Developer Eyedropper to grab the RGB from a photo of an Edison Light Bulb. #FACA08 (250,202,8) A lighter pixel This is very close to the color when a 2700K 97 CRI LED was reflected off bright white paper: #F4D4AB (244,212,171) just a little less blue. #F5D483 (245, 212, 131) I do not believe the LED actually illuminates ...

8

LEDS actually come in all colours. However, what we as humans call colour is dictated by the fact that the cones in the human eye are only actually sensitive to three primary groups of wavelengths which we call red, green, and blue. Different LED technologies produce light in a similar but narrower bell curves around a particular wavelength. When we look ...

8

Without knowing the schematic im going to just guess these are standard 5050 leds put in a 3 led series setup. For purple you need Red and Blue 100% on. For white you need Red Green and Blue 100% on. Since your source voltage is much lower than the typical 3.2 to 3.6V forward voltage for a blue led diode time 3 ( 9.6 to 10.8) , thats an issue. You need to ...

7

For a single LED you are correct - which side you put it on does not matter. However, an RGB LED is a rather different animal since one side of all of the elements are tied together. This presents a bit of a problem. If you wire the common terminal directly to a power rail and put 3 resistors on the other side, it will work as expected. However, if you a ...

7

LEDs of different colors are made with quite different materials and processes and designs. There's no guarantee that they'll turn out to be the same brightness. It makes more sense to put more efficient LEDs in there when they are available rather than degrade the more efficient ones in order to match the least efficient color. Sure they will have to run at ...

7

Composite video signals are usually AC coupled, so you shouldn't need to pull the output below ground. The receiving end will restore the DC level (using the sync pulse as a reference) if it needs to. At the input side the signal may go below ground - or not, depending on the source. To cover all possibilities you should terminate the input with 75Ω ...

7

Using an LTspice simulation with 100 MHz 0.5 V peak sine wave input and the Figure 36 unity gain buffer (+/-5 V supplies), and a 20 pF load, I get about 130 ps. You can see from Figure 5 (in the datasheet) that it is much less than 1 ns.

7

LEDs, like all diodes, have reverse leakage current. Because of this leakage, with the common anode left open, if one or more of the cathodes is at a positive voltage (that is, the 'off' state) the common anode will bias to some midpoint voltage, which will leak to the diodes that are in the 'on' (cathode grounded) state. This leakage can be enough to make ...

6

Start by scaling the R,G and B by the intensity value, for your example at 50% intensity you would set 15*0.5, 170*0.5, 230*0.5 (7, 85, 115). The LEDs might have different non-linear responses, so you might need to tweak the scaling for perceived colour In particular, at very low levels, you will suffer from rounding error. There is no easy way around ...

6

You are attempting to map a triplet of values (the responses of the LDR to your RGB LEDs) to another triplet (the RGB values you used to print the colors on the paper). There are loads of environmental values that will influence this mapping. IMO the best you can do is Make sure each LED gives a decent and compareable effect. Depending on your LEDs and the ...

6

Single LEDs come in orange, yellow, amber, infrared, ultraviolet, cold white, warm white and many other colors/hues. Therefore I assume you mean to ask why multicolor LEDs are typically red, green and blue. The answer lies in how colors are mixed. Additive color is color created by mixing a number of different light colors, with shades of red, green, ...

5

The red, green and blue of RGB LEDs do have different perceived luminous intensities, for several reasons. Some of them are listed below, not in the order of importance: Eye color sensitivity The human eye is sensitive to different colors to different levels - and this relationship also varies by light intensity: Both ambient light intensity (bright room ...

5

The 100mA/10% duty cycle is absolute maximum rating at 25°C ambient temperature. It is not something you should be designing to, and note that it only gives you 10mA average current per LED. It should be derated significantly (let's say 30%, 40% or more) to allow for ambient greater than 25°C and to avoid the absolute maximum limit. At 40% derating, you can ...

5

Light sensors aren't limited to any distance. It makes no difference whether the photons they sense came from someone's clothes 1 foot away or the sun 93 Mmiles away. Your problem with distance is probably that the light is not focused, so the sensor is seeing the average of a large angle. When a person is close, that angle of view will be dominated by ...

5

Your result isn't a matrix of MxNx3. Your result is a sequence of numbers. You can store them however you like. Take the LCD screen you're reading this on, for instance. That is a 2D device, isn't it? Yet it looks like it would have a display of MxNx3. Look closer though. Very close. Get a magnifying glass and look reeeeeeal close. It's actually a ...

5

Computers detect screens by something called Display Data Channel It's a low rate data signal on four pins in the VGA connector that tells the computer about its presence, allowed modes and frequencies, etc. You can still use a screen without DDC, but you need some pull-up or pull-down resistors to tell the computer there's a screen at all. You'll also ...

5

To understand the results you are getting you have to consider the spectral response curves of your light source, detector, and the object being measured. The final result is a combination of all these 'filters' acting on the signal. And if you want to relate that to the colors you see, then you also have to take into account the spectral response of the ...

5

Simple. Different colors correspond to different wavelengths of light, shorter wavelengths of light require more energy, producing photons of higher energy requires a larger bandgap in the semiconductor, and a larger bandgap produces a larger voltage drop. All of this means that Vf of a blue LED is the largest, green is in the middle, and red is the ...

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