Illumination means to "shine light onto something" - like a flashlight or headlights. You want your headlights to be bright as heck.
Brake lights should be bright enough to see, but don't need to light up the road!
Indication mean to "point something out" - like a turn signal or brake lights on a car. You don't want your car's turn signal to blind people!
If you get the wrong type you could end up with a DIY flashlight that is dim, or a control panel that burns people's eyes!
Diffused LEDs are really good at indication, they look soft and uniform and you can see them well from any angle.
Clear LEDs are really good at illumination, the light is direct and powerful - but you can't see them well from an angle because the light is only going forward.
Let's verify this. On this breadboard I've connected two LEDs, one Red Diffused and one Clear Bright Blue LED. Both have the same resistor (which means they're basically using the same amount of power). You should follow along, wiring up one of each. Use a 1.0K or so resistor from the cathode (shorter pin) to Ground and connect the anode (longer pin) to +5V.
Probably not visible in daylight.
You can easily look at these
You can look at these if you're more than a few inches away, otherwise you'll see spots.
You can look at these if you're more than a few inches away, otherwise you'll see spots.
Looking directly at this is not pleasant.
Don't look straight at these, it'll hurt your eyes.
Changing the brightness with resistors
Lets go back to our basic LED setup: one LED and one resistor connected from 5V to ground. This time we will duplicate it so that we have three LEDs except that each resistor is going to be different. LED #1 will have a 100 ohm resistor (Brown Black Brown), LED #2 will have 1.0K (Brown Black Red) and LED #3 will use a 10K (Brown Black Orange).
Changing the brightness with voltage
Having learned a little about how to use resistors to change the brightness of an LED, we will now try experiment #2. This time we will use only 1.0K resistors but connect the anodes to different voltages. One LED anode will go to 3.3 volts another will go to 5.0 volts and the third will go to Vin (which, if you have one of our starter packs, goes to a 9V wall adapter, so its 9.0 volts
Max brightness!?
Lets do another quick experiement. Lets say we had a magical resistor with a knob, that we could change the resistance of from 0 resistance (like a piece of wire) to infinite resistance (something that does not conduct, like rubber).It would seem, then, that if we want a really really bright LED, we should just use a zero ohm resistor and connect to the highest voltage we can, right? And who wouldn't want an LED thats as bright as possible?
Lets build an LED circuit with a zero ohm resistor (also known as a wire) to Vin so be sure to plug in the Arduino into the wall with a plug-pack/wall-wart. (For somewhat detailed reasons we'll cover in another tutorial, using the 3.3V or 5V power pins won't do what we want, we need to use Vin).
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