To read the graph, imagine the LED is standing upright underneath it. Some LEDs are like floodlights that pump out photons in every direction Others are so directional that you can't tell they're on unless you're looking straight at them. Different styles of LEDs will incorporate lenses and reflectors to either concentrate most of the light in one place or spread it as widely as possible. Next, we've got this fan-shaped graph that represents the viewing angle of the LED. At 200 mcd, this LED would make a good indicator. This LED has an maximum intensity of 200 mcd, which means it's just bright enough to get your attention but not quite flashlight bright. The unit mcd, or millicandela, is a standard unit for measuring the intensity of a light source. The last row (labeled "Luminous Intensity") is a measure of how bright the LED can get. Again, we'll go over wavelength in more detail in the delving deeper section. In this case it's 620 to 625nm, which is just at the lower red end of the spectrum (620 to 750nm). There may be some variation in this number so the table gives us a minimum and a maximum. Wavelength is basically a very precise way of explaining what color the light is. The second row on this table tells us the wavelength of the light. We'll talk about this more in-depth later in the delving deeper section of this tutorial.
If you have more than one LED connected to a single power source, these numbers are really important because the forward voltage of all of the LEDs added together can't exceed the supply voltage. This number will help you decide how much voltage your circuit will need to supply to the LED. Forward voltage is a term that will come up a lot when working with LEDs. This is a useful little table! The first row tells us what the forward voltage drop across the LED will be. Let's see what other kinds of tables they've put in here. This should work itself out as long as you keep the LED within its suggested voltage and current ratings. The power dissipation is the amount of power in milliWatts that the LED can use before taking damage. The reverse voltage is a diode property that you shouldn't have to worry about in most cases. The following few rows are of less importance for the purposes of this tutorial. That's a good target number to help you make the resistor calculations we talked about. This datasheet is even helpful enough to suggest a stable current range (in the third row from the top) of 16-18mA. This LED can handle short bumps to 30mA, but you don't want to sustain that current for too long. The second row tells us what the maximum peak current should be for short bursts. In this case, you can give it 20mA or less, and it will shine its brightest at 20mA. The first row in the table indicates how much current your LED will be able to handle continuously. You can find out all about it in the example applications of our resistor tutorial! Don't worry, it only takes a little basic math to determine the best resistor value to use. Resistors limit the flow of electrons in the circuit and protect the LED from trying to draw too much current. That's why it's important to limit the amount of current flowing across the LED.įor this, we employ resistors. If you connect an LED directly to a current source it will try to dissipate as much power as it's allowed to draw, and, like the tragic heroes of olde, it will destroy itself. 3) There is Such a Thing as Too Much Power But, setting the mood isn't the only reason to cut back your current.
The second is that you can control the brightness of an LED by controlling the amount of current through it.
The first being that super bright LEDs drain batteries more quickly, because the extra brightness comes from the extra power being used. The brightness of an LED is directly dependent on how much current it draws. So don't freak out if adding an LED breaks your circuit. A reversed LED can keep an entire circuit from operating properly by blocking current flow. The other, negative side of the LED is called the "cathode." Current flows from the anode to the cathode and never the opposite direction. The positive side of the LED is called the "anode" and is marked by having a longer "lead," or leg.
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