Component of the Month: LEDs and Diodes

Light-emitting diodes (LEDs), as well as diodes of the non light-up variety, are the topic for June’s Component of the Month coverage.

We kick off June with an excerpt from Syuzi Pakhchyan’s excellent resource for wearable tech, Fashioning Technology.

Want to learn more about LEDs and diodes? We’ll be covering them all this month.

LEDs (light-emitting diodes), the modern craze in lighting, hold the promise of making obsolete Edison’s greatest invention, the incandescent light bulb. They are in toys, in automobiles, in stop signs, in every color-shifting gadget, and are even being added to clothing. These techno-sequins are arguably the greatest crafting material invented.

Why are LEDs so darn cool? First of all, they are compact and emit bright light lasting as long as 10 years. Secondly, unlike traditional light bulbs, they don’t get hot. And most importantly, they consume very little power. This means that you can continuously run a super-bright LED off of a small battery for more than a hundred hours.

LEDs come in several colors, brightness levels, sizes, and shapes. The two types of LEDs that you will use in these projects are standard LEDs and high-flux LEDs. These and several others are discussed in detail at the end of this section. Before you start working with LEDs, there are a few essentials you need to know.

Understanding the Technical Specifications for LEDs

Following is an explanation of all the technical data and symbols that come with your LED package. With an understanding of a few basic terms, you will be able to easily choose the right LED for your project and use online resistor calculators to determine the right resistor for your circuit.

Forward Voltage (V_F): Also referred to as the forward voltage drop, the VF is the minimum amount of voltage needed to light up an LED.

Luminous Intensity (I_V): The IV is the amount of light emitted from an LED in a particular direction. It is measured in millicandela (mcd). For our purposes, consider luminous intensity the “brightness” of an LED. The greater the millicandelas, the brighter the bulb.

Forward Current (I_F): IF is the amount of current an LED uses.

Viewing Angle: The viewing angle is the spatial distribution or spread of light. It is expressed in degrees that measure the width of the light beam. LEDs with a small viewing angle produce a more focused beam, and LEDs with larger viewing angles produce a softer, more dispersed beam.

Different Types of LEDs

There are a plethora of LEDs on the market, ranging in color, shape, brightness, and viewing angle. This is an overview of the different types of LEDs and their characteristics to help you determine the most appropriate type for your projects.

Bicolor or Tricolor (RGB) LEDs

• Two- or three-colored LEDs sandwiched into one housing.
• Bicolor LEDs (Fig. A) have three different-length leads, sharing either a positive (anode) lead or a negative (cathode) lead.
• Refer to the data sheet to distinguish the leads, or create a simple circuit using a pair of alligator clips, a battery, and a resistor (see page 29).
• Typically, in bicolor LEDs, only one of the colored LEDs can be lit at a time.
• Tricolor (RGB) LEDs, seen in Figure B, combine red, green, and blue color spectrums, and when mixed together can reproduce a wide range of colors.
• RGB LEDs have four different-length leads, sharing either apositive lead or a negative.
• Typically, a microcontroller is used to program an RGB LED to gradually shift from one color to the next.
• Rare but available from a small number of retailers are RGB flashing LEDs that are preprogrammed to blink and fade from one color to the next.

Blinking/Flashing LEDs

• Blinking/Flashing LEDs (Fig. C) have similar characteristics to standard LEDs, except that they contain an integrated circuit (IC). This IC blinks the LED (turns it on and off) intermittently at predetermined time intervals.
• Designed to be directly connected to a power supply, eliminating the need for a resistor.

Infrared (IR) LEDs

• IR LEDs (Fig. D) Emit infrared light that is invisible to the human eye.
• Typically coupled with an IR receiver/sensor (aka detector) that recognizes the infrared light and translates it into an electrical signal.
• The most common example is found in your remote control.

Piranha or High-Flux LEDs

• High-Flux LEDs (Fig. E) are square with four leads: two positive and two negative. As all four leads are the same length, to distinguish the positive from the negative you must either refer to the LED’s data sheet (usually available as a PDF download online) or create a simple circuit using a pair of alligator clips, a battery, and a resistor.
• Available in a number of colors, brightness levels, viewing angles, and a few select sizes.
• Practically all come in a clear case and are brighter than typical LEDs.

  Great for sewing applications, as they can be positioned flush to fabric and their leads are pliable–able to be bent easily and sewn.

Standard LEDs

• Standard Leads (Fig. F) have two leads: a positive and a negative. Typically, the long lead is the positive (the anode) and the short the negative (the cathode).
• Available in different shapes, sizes, and colors. Normally range in size from 3mm to 10mm and come in red, orange, amber, yellow, green, turquoise, blue, and white. Pink and violet LEDs are rare but also available.
• Come in a colored, water-clear, or diffused epoxy resin case. Either round, flat, or square in shape.
• Apart from their physical properties, they are available in different levels of brightness, measured in millicandela (mcd), and in different viewing angles.
• The brighter the LED and the greater the viewing angle, the more expensive the LED.

Surface Mount Device (SMD) LEDs

• SMD LEDs (Fig. G) are tiny, rectangular LEDs with two copper contacts: a positive and a negative. On the back side there is a green arrow or line indicating the negative contact.
• Available in a number of colors, brightness levels, viewing angles, and sizes, SMDs provide the best package in terms of size and brightness.
• The downside is that they are relatively difficult to work with because they are so tiny. But with a little bit of patience and soldering skill, you will be soon incorporating SMDs into your projects.

Ultraviolet (UV) LEDs (aka Blacklight LEDs)

• UV LEDs (Fig. H) emit invisible UV-A rays ranging between 345nm and 400nm.
• When used with fluorescent or phosphorescent materials, produce an interesting light-emitting effect, causing bright objects to glow.