Tips and Tricks - Adding LEDs (Part 2: LED properties)

A light-emitting diodes, also known as an LED, is a semiconductor light source. It emits light in response to the passage of electric current. The color of the light that it emits corresponds to the energy of the photons released, which is determined by the energy gap of the semiconductor. A diagram of what makes up an LED can be seen below.

For the most part, you don't need to worry about any of that, but there are some properties of LEDs that you do need to be aware of.

Lens/Case - Casings come in the flavors, clear, colored clear, and a diffused colored. The diffused colored LEDs allow for a uniform distribution of light. The colored clear cases are used for a more focused light. Clear cases give the purest form of light. In the diagram above, you can see that the casing is often much larger than the diode. This means that if the case does not fit where you need it to, it can be trimmed. Be sure to not damage any of the diode components while trimming. If you do try to trim the casing using a hobby knife, be careful as it can chip and crack.

Color/Wavelength - This property determines what color the LED will give off.Values and the corresponding values are:

• Violet: 390-450 nm
• Blue: 450-475 nm
• Cyan: 476-495 nm
• Green: 495 - 570 nm
• Yellow: 570 590 nm
• Orange: 590 - 620 nm
• Red: 620 - 750 nm

If you're looking to have a black light effect, you can find LEDs in the ultraviolet spectrum which ranges from 315 to 400 nm.

Forward Voltage - This is the voltage required to power the LED. For your standard green LED, this values is around 2V. Remember when selecting a battery, to go above the value for the resistor.

Maximum Current - This is the maximum current the diode can handle without risking damage. This value will be used to determine the size of the resistor.

Luminous Intensity - This is essentially the brightness of the LED. Generally, this is measured in milli-candela (mcd). The higher the number, the brighter the LED. Below, is a comparison. On the left, is an LED purchased from RadioShack with an mcd value of 20. On the right is a Gunpla Green LED. I'm unsure of the mcd value, but my guess is it's somewhere around 5000.

Where to buy - I would not recommend getting LEDs at RadioShack. Instead, I would recommend looking online. Amazon has a few stores with various LEDs. They may be a little over priced, but you can often select different shipping methods and you have the protection of Amazon with your order. A Google search can turn up a few online stores. In my searching these tended to be more expensive, but you are able to contact the seller for questions and special requests. Lastly, there is ebay. The prices here are the best I have found. More often that not, the shipping is free. However, they often ship from Hong Kong so depending on where you live will determine how long it take for you to receive them.

In the next part, I will be going over the basics of circuit design.