Since the invention of electro-optical light-emitting diodes or LEDs in the 1960s, these devices have found numerous uses. An LED offers a great many benefits that other technologies simply cannot match. From their use in different kinds of monitors and displays to consumer illumination in advertisements, there are many uses you are undoubtedly familiar with. Further, LEDs are also used in laboratories and for industrial applications.
There is a large range of options available, so you can use some tips on choosing the right LED and configuration for your needs.1. Viewing Angle
LED lights are generally bright, but the angle at which you or the end user will view the display also matters. In many cases an LED features reflective surfaces, and this can concentrate the luminescence into certain angles. However, these can seem dim from the sides. With a wider viewing angle you can often increase the degrees of easy viewing.2. Power Consumption
How much power are you going to have available? How much can you use? Adjusting the power consumption can conserve batteries or outlet power, which can be very cost effective for the end user. It is also important to stay within the parameters the manufacturer specifies for the LED. Running more than the recommended amount of power through an LED is possible, but it will shorten the operational lifespan of the diode.3. Efficiency of Use
LED lights have their light measured in micro candelas (for the visible range) which is a luminous intensity. A candela measures how much power is emitted in a particular direction, and then adjusts this to how sensitive to visible light the human eye is. With greater efficiency, the LED will generate more light per Watt of electricity run through it. There are both standard LEDs and super bright ones. As well, there are even ultra-bright LEDs for specialized purposes.4. Total Power
Power consumption is a serious matter. Just like running too much through an LED will damage it, not running enough may not allow for your intended purpose. A high power LED may consume 1 W of power at once, while lower power units may only consume 100 mW during the same period. The cost savings can add up tremendously over time.5. Color options
Today, LEDs come in numerous different colors. With amber, green and red being the old standbys, blue, violet and white are now also available. With so many “white” diodes being made of NUV or blue diodes filled with several kinds of phosphors, the combination of blue and phosphors makes a light that appears to be white. Often, this is a blue pump diode that operates in the 460 to 470 nm range, and this is combined with a phosphor in a broad range with an emission that centers near 540 to 550 nanometers. Unfortunately, the lack of cyan and red in these LEDs can render skin tones, artwork, flowers and fabrics poorly.
Fortunately, lighting applications have led many LED suppliers to provide red output from auxiliary red LEDs to compensate for this. With NUV pump diodes, often three different RGS phosphors are the main suppliers of the light and the blue makes very little contribution to white light. Often, this results in a more balanced distribution across the spectrum, and this also corresponds to a higher CRI.
It is possible to make RGB LED white lights, but this is uncommon due to the difficulty of color matching three LEDs properly. With the input current, the temperature, the output and color all contribute to making a consistent color output challenging without some manner of closed loop feedback being required.
Continuous and arbitrary color selection is thus the main application for RGB LEDs. There are some drawbacks, such as the intermediate colors that fall between the spectrums that each LED can work within. This can create metamerism problems that also sometimes happen with phosphor-based white LEDs. Some companies prefer RGB lights because of the high saturation they can provide.
The activation energy within the semiconductor materials it uses determines the color of the LED in question. Some examples are GaN for blue, GaAsP or InGaA1P for red, and GaP for green light.6. Drivers of LEDs
Consistent illumination and higher lifespans in LEDs require the right level of current as specified in their spec sheet. A simple way to make this happen involves an LED driver. Such a constant current supply is designed for LEDs, but this does require matching the driver to the correct LED. A pulsing width modulation can produce a dimming effect, as this activates and deactivates the LED faster than a human eye can identify. All this dimmer function requires is a shorter cycle of duty.7. Packaging
An LED can come in many types of physical packages. Generally, they come in 3 mm, 5 mm and 8 mm versions of round top cylinders. Often, a 7-segment package works for displays, especially those used in time pieces, as a 7-segment decoding IC chip produces the correct number based on the digital signal it receives.8. Multiple packages
Several LEDs can be purchased within one package. This can include strips or strings of LEDs in one row or even with several displays. This can save on the circuit complexity and the time required to properly engineer the desired effect. Often, one power source or a control IC can drive the entire group. Often, the current and power requirements will be different for devices that use multiple LEDs.9. Included controls
An LED can be in a package that involves unique control circuitry that is built directly in. This can include a stable multivibrator circuit that makes the LED blink, or can even use different timing patterns. In a similar vein, an LED may be packaged with a current limited resistor. This can use a certain range of voltage, which can save space on smaller boards and can be convenient for more compact applications.10. LEDs are not always the best option
An LED is great for many types of applications. However, coherent light may be better suited to sources such as a laser.
Let us know if we’ve missed any useful tips that you may need for your selection process.