Let’s get Physical
Types of LEDs
Now that we know what an LED is and have an over-simplified understanding of how they work, let’s take a look at something a little more concrete. Note that this isn’t an exhaustive list of LED types, just some of the more common ones.
The through-hole LED is probably the most common you’ll encounter on game consoles. They have two (sometimes more more in the cases of dual-color LEDs and RGB LEDs) leads that poke through a via on a PCB and are soldered on the opposite side.
Surface mount (SMD)
Unlike their through-hole counter part, surface mount LEDs are solder directly to the top layer of the PCB via contact pads. If you’ve ever seen SMD capacitors or fuses, SMD LEDs are soldered the same way.
I’ve never seen a game console that came from the factory with strip LEDs but they’re quite popular with modders. The LED strip itself is made up of many surface mount LEDs which do not need to be soldered directly to a PCB the same way stand alone SMDs or through-hole LEDs do. Instead, the strip will have contacts that can be attached directly to a power source. They’re great for illuminating areas that don’t necessarily have a place to mount traditional LEDs and can be adhered with sticky tape or hot glue.
Just like other diodes, LEDs have a positive input (Anode) and negative output (Cathode). On through-hole LEDs, one of the leads will be longer than the other – this is the positive/anode lead. Surface mount LEDs are a little trickier to tell anode from cathode. Often times there will be a notch, dot, or some other marker such as the “plus” sign +.
Current and Voltage
Different types of LEDs have differing forward current requirements. For the vast majority of LEDs you’ll encounter on game consoles will be 3MM and 5MM in size, which should receive a maximum of 20 milliamperes (mA).
Based on wavelength (remember, wavelength is color), we can determine the forward voltage required to power the LED. These values in the below chart are approximate and will vary between manufacturers.
|Color||Forward Voltage at 20mA|
|Red||1.8 – 2.0|
|Orange||2.0 – 2.2|
|Yellow / Amber||2.0 – 2.2|
|Green||3.2 – 3.4|
|Cyan||3.2 – 3.4|
|Blue||3.2 – 3.4|
If the current or voltage is too high, you’ll shorten the life of the bulb or worse, burn it out immediately – this is called electrical over stress (EOS).
The brightness of an LED is measured in “millicandela”, MCD. The higher the MCD value, the brighter your bulb will be. You might think that the more voltage applied to the bulb will cause it to be brighter but this isn’t necessarily the case. Current, however, will effect brightness but as mentioned above, too much current will burn out your LED, literally.
There are 2 other factors to consider for LED brightness, and that is viewing angle and diffusion.
Diffused LEDs have bulbs that have given a dense coat (sometimes referred to as “milky”) to help reduce the brightness but at the same time dispersing it in a broader direction. This contrasts non-diffused (clear) LEDs where the light emitted is more direct.
Can’t talk about LEDs with out talking about resistance. We’ll cover resistors and Ohms on the next page.