About LEDs
-
What are LEDs?
-
What are LEDs used for?
-
Which purchase criteria make it easier to select the right LED?
-
Conclusion
What are LEDs?
An LED or light-emitting diode is a modern illuminant and is regarded as a future-proof lamp in the field of lighting technology. It functions like a semiconductor and has a single forward direction for the current. A diode can produce infrared, ultraviolet, and light. The normal LED is operated at 20 mA. High-power LEDs require a larger power source and must ensure increased heat dissipation at the same time. If the operating temperature is too high, the luminosity will deteriorate and the service life will be shortened enormously. High-performance LEDs are often used for mounting on heat sinks.
Construction
The wires of a diode are called cathode and anode. The cathode belongs to the negative pole of the diode and is the shorter of the two wires. Thus the anode is positive and the longer wire. It is rare that the design of the wires is reversed. Wired LEDs are one of the first LEDs on the market. They usually have a low-performance chip, which is why they are often used for signal display. Multiple wired light emitting diodes are used in LED spots and other light sources, as better semiconductors favor the performance of the chips. The advantage of wired LEDs is that there is little heat dissipation and soldering is very simple.
An LED has different lens shapes. Some variants are flat-edged lenses, curved, triangular, oval lenses and the bell-shaped lens. Each lens has a different viewing angle and light yield. In addition, you can choose between clouded and clear lenses. Standardized LED lenses have a diameter of 5 mm.
Properties
Light emitting diodes emit a light that is almost monochromatic. Therefore, LEDs are particularly suitable as signal lamps in comparison to conventional bulbs. Monochrome light describes a single-color visible light. In the electronics sector, it refers to electromagnetic radiation on a specific wavelength or frequency.
The light is proportional to the operating temperature. If the temperature increases, the light intensity increases. To determine a clear luminosity, a constant current source is the best solution. Standard LEDs can easily accept a current of between 2 mA and 20 mA. In many cases, a power of 10 mA is sufficient to light up the diode. A low-current LED has the property of lighting up from 2 mA. The luminosity does not correspond to the same with a 20 mA operation.
High-power LEDs work up to 18 ampere. Voltage drops in LEDs can be observed due to the semiconductor material and series resistors. The flow voltage UF also depends on the material. The term IF stands for the flow current of an LED. The recommended values for the voltage drop are:
-
Infrared LED 1.2 – 1.8 V.
-
Red LED 1.6 – 2.2 V
-
Yellow, green LED 1.9 – 2.5 V.
-
Blue, white LED 2.7 – 3.5 V
-
UV LED 3.1 – 4.5 V.
LEDs are battery-dependant and therefore have a maximum permissible reverse voltage of 5 V. A higher reverse voltage can already lead to the LED failure.
Another important aspect is the opening angle of an LED. The opening angle determines the radiating power from the lens. Unlike other illuminants, only one face can be illuminated due to the opening angle. Straw-hat-LEDs denote LEDs with a lens for larger opening angles.
The lifetime of an LED is determined by the luminous flux. The light intensity decreases steadily during the life cycle. A sudden failure can usually be ruled out. Higher temperatures shorten the life of a diode.
Why is a series resistor required?
Do not connect an LED to a direct voltage as it is sensitive to excessive flow. The semiconductor material makes a series resistor indispensable. The natural resistance of a semiconductor decreases when powered to zero. Without a series resistor, the LED would draw more and more current and become hotter as a result. In addition, a temperature rise increases the characteristic of the semiconductor to conduct even more current at heat. A circuit occurs that leads to the final destruction of the LED after a low light time.
The series resistor weakens the flow rate and thus enables smooth operation. In rare cases, a series resistor can be dispensed with. Voltage sources with high-resistance internal resistances act like a series resistor for the LED. Any series resistor that limits the current to a value of no more than 20 mA is suitable for use with an LED.
What are LEDs used for?
In the early years of development, light emitting diodes were often used in infrared controls and light barriers. Since the market launch, they have been increasingly used in room lighting, street lighting, torches, LED lights, flash lights on smartphones and cameras or in LED strips. LED strips are used for indirect and invisible lighting. High-power LEDs are increasingly used in traffic lights and vehicle lights.
Which purchase criteria make it easier to select the right LED?
Lens shape
The lens shape is responsible for the light emission angle. Depending on the type of lighting required, oval, triangular and curved lenses can be selected. Flattened flat-edge lenses are also available.
Light intensity
The light intensity is given in "mcd". The designation serves as a physical indicator for the brightness of the LED. Simpler: "Mcd" is the unit that determines how well the human eye absorbs the light. 1000 mcd corresponds approximately to the brightness of a candle. The guide value is
• Candle light = 150 watts = 15 lumens
• 1W LED = 1W = 90 lumens
Angle of radiation
The diameter of the beam is influenced by the angle of radiation. The larger the angle of radiation, the larger the diameter of the light cone. Radiation angles of 120° are suitable for living spaces. For corridors or similar paths a beam angle of 90° is sufficient. The selection of the correct beam angle depends on the location and application.
The color temperature
The color temperature for the illuminant is indicated in Kelvin. Color temperature information is essential for correct selection of the required light source. Light colors according to DIN 5035 are:
• Warm white: In Kelvin: Below 3300 K
• Neutral white: In Kelvin: 3300 – 5000 K
• Daylight white (cool white): In Kelvin: 5000 K.
Conclusion
Wired LEDs are particularly suitable for use as signaling devices or for lighting individual areas, for example in vehicle cockpit. The angle of radiation in combination with the lens shape determines the basic light range of an LED. Radiation angles of 90° or 120° are often used for rooms. Small radiation angles are suitable for signal lights, but should not be smaller than 45°. The series resistor increases the service life and controls the power supply. As the upper limit, the resistance must not allow more than 20 mA at current.
What are LEDs?
LEDs now meet us everywhere: Whether traffic lights, television or lighting in private and business rooms. Due to their long life, their small size as well as the variety of shapes and color spectra, LEDs have become established in a short time as compared to light bulbs, halogen and energy-saving lamps. Behind each LED there is a whole piece of technology, which we explain to you in our guide.