SMD LEDs
(6 004)SMD LEDs (i.e. diodes intended for surface mounting) are among the most popular optical electronic components. They are used in backlighting and indicator components, for making large and complex arrays in LED light bulbs, tubes, strips, and more. The great advantage of SMD LEDs is their small size, thanks to which they can be used in mobile devices (flash lamps and torches in mobile phones are good examples here). Moreover, SMD diodes are also parts of LCDs, where they backlight the screen.
The SMD LEDs often have similar, if not identical, parameters to the THT components. These features also make them very popular. Nevertheless, small optoelectronic components can get overheated – especially in applications that involve illuminating objects. Therefore, as a designer and installer you should always take into consideration proper cooling of LEDs (ensure an adequate airflow or adhesion to the surface of a heat dissipation element, such as a copper heatsink or aluminium mounting strip).
In DIY projects or prototype development, using SMD LEDs may be more complicated. Luckily, you can choose to use THT components in the circuit in the designing phase, and then replace them with smaller equivalents in the final version of the device.
What are typical applications of colour SMD LEDs?
The SMD LED category has three product groups: white and coloured components and light pipes (light guides). Colour SMD LEDs are typical indicator components. SMD LEDs are often chosen for two main reasons: to minimise the PCB footprint occupied by optoelectronic components and to avoid drilling holes in the board. If the entire circuit was made using the SMD technology, a THT component would be a suboptimal choice. However, compact light sources have their shortcomings, too. Above all, they are positioned in parallel to the PCB surface and have a relatively small face area. To overcome these, one can use special light pipes for LEDs. They are transparent optical components which transfer light to the desired spot. The light pipes are designed for mounting on PCBs, and their light output is perpendicular to the input site. Due to this, LEDs may be mounted on the motherboard of the device, and the emitted light is visible to the user (e.g. at the front panel).
Colour LEDs category also comprises multicolour components, including RGBs. They emit mixed red, green and blue light, which (depending on relative intensity) may produce any light colour. To control such components, PWM signals are used. In order to achieve a uniformly coloured light, one may use light-diffusing components. There is also a special variant of multicolour components, namely RGBW devices, which can also emit white light.
Advantages of SMD LEDs emitting white light
Unlike the colour LEDs, white SMD LEDs are usually used as light sources. Of course, they may also be used as indicator lights – for example, in electronic and household equipment. Moreover, TME also offers LEDs with relatively high power (up to 1 W), intended for use in illumination systems, light sources and special effect installations. Due to their excellent energy efficiency, such components are often applied in battery-powered devices: low-power white SMD LEDs are used, for example, to illuminate keyboards in laptops, while brighter components are installed in torches or power tools. It is worth emphasising here that LEDs intended for interior lighting i.e. power LEDs, are listed as a separate TME catalogue category.
White light is characterised by one crucial parameter, namely its colour temperature. Even a tiny difference in the wavelength of the emitted light translates into the human perception of light as “warm” or “cold”. The value is expressed in K (kelvins). White light in the colour temperature of 5000–8000 K is similar to daylight. Below 5000 K, light becomes yellowish (1000 K is the colour temperature of a fire flame), and above 8000 K, light becomes blueish.
When power light sources are used, the produced heat must be dissipated to avoid overheating the system. A single SMD LED (even a very small one) may produce light with the intensity of over 135 lm. It is brighter than a traditional 10 W lightbulb. An LED consumes considerably less power than a standard lightbulb (e.g. 1 W), but due to its tiny dimensions, the component may heat up considerably, and its temperature may be harmful to the human body and deform plastic parts.
Crucial parameters and markings of SMD LEDs
The selection process for SMD LEDs is identical to that for components enclosed in other types of casings.. The only significant difference is the coding scheme, which is typical for other SMDs. According to the scheme, a four-digit symbol describes the size: the two first digits denote the length, and the two last ones – the width of the component. The unit is 0.01 in. An alternative, metric system for SMD markings is analogous to the former, but the unit is 0.1 mm. The majority of optoelectronic components are manufactured in standard sizes. There are, however, some exceptions to this rule.
The remaining parameters of the LEDs are consistent, regardless of the scheme. The operating voltage and current describe the LEDs electrical characteristics and also facilitate the selection of a current-limiting resistor. Power describes the energy consumed by the component. Viewing angle describes the lens used: depending on the application, the designer may decide to use an LED with a narrow viewing angle (10–20°) or a very wide one (up to 180°) so that the light can be seen along a line that is almost parallel to the PCB surface. LED colour may be defined in two ways: in general (by the name, “red”, “green”, etc.) or by referring to the specific wavelength of the emitted light. For white LEDs, an important parameter is luminosity, denoted in lumens (lm) and sometimes millilumens (especially in the case of indicator components).
Warehouse:
