According to Abbreviationfinder, LED stands for Light Emitting Diode.
Infrared emitting diodes (IRED) are used since the mid-twentieth century in remote controls for televisions, having widespread use in other appliances such as air conditioners, stereos, etc., and in general for applications remote control and as in detecting devices, in addition to being used to transmit data between electronic devices such as in computer networks and devices such as mobile phones, handheld computers, although this data transmission technology has given way to bluetooth in recent years, becoming almost obsolete.
LEDs are widely used in all kinds of status indicators (on / off) in signaling devices (traffic, emergency, etc.) and in information panels (the largest in the world, from the NASDAQ, is 36.6 meters high and is in Times Square, Manhattan). They are also used in the lighting of liquid crystal displays of mobile phones, calculators, electronic agendas, etc., as well as in bicycles and similar uses. There are also printers with LEDs.
The use of LEDs in the field of lighting (including traffic signaling) is moderate and it is foreseeable that it will increase in the future, since its performance is superior to that of the incandescent lamp and the fluorescent lamp, from different points of view. view. LED lighting has undoubted advantages: reliability, greater energy efficiency, greater resistance to vibrations, better vision under various lighting circumstances, less energy dissipation, less risk to the environment, ability to operate continuously intermittently, quick response, etc. Likewise, with LEDs it is possible to produce lights of different colors with a high luminous efficiency, unlike many of the lamps used until now. that have filters to achieve a similar effect (which means a reduction in their energy efficiency). It should also be noted that various tests carried out by important companies and organizations have concluded that energy savings vary between 70% and 80% compared to the traditional lighting that is used until now.  All this highlights the many advantages that LEDs offer in relation to public lighting.
White Light LEDs are one of the most recent developments and can be seen as a very well founded attempt to replace current light bulbs(incandescent lamps) with much more advantageous devices. Technology is currently available that consumes 92% less than common household incandescent bulbs and 30% less than most fluorescent lamps; In addition, these LEDs can last up to 20 years and represent 200% lower total cost of ownership when compared to conventional fluorescent bulbs or tubes. These characteristics make White Light LEDs a very promising alternative for lighting.
They are also used in the emission of light signals that are transmitted through fiber optics. However, this application is in disuse since currently laser technology is chosen that focuses more light signals and allows a greater range of the same using the same cable. However, in the early days, fiber optics were used for their low cost, since they were a great advantage over coaxial (even without focusing the light emission).
LED screen: very bright screen, formed by rows of green, blue and red LEDs, arranged according to RGB architecture, individually controlled to form vivid, very bright images, with a very high level of contrast, among its main advantages, compared to others screens we found: good color support, extremely high brightness, which gives it the ability to be fully visible under sunlight, is incredibly resistant to impacts.
To connect LEDs so that they illuminate continuously, they must be directly polarized, that is, with the positive pole of the power supply connected to the anode and the negative pole connected to the cathode. In addition, the power supply must supply you with a voltage or potential difference greater than your threshold voltage. On the other hand, it must be guaranteed that the current flowing through them does not exceed the admissible limits, which would irreversibly damage the led. (This can be done easily with a resistor R in series with the LEDs). Some simple circuits that show how to directly polarize LEDs are as follows:
The potential difference V d varies according to the specifications related to the color and the supported power.
In general terms, the following potential difference values can be considered roughly: 
- Red = 1.8 to 2.2 volt.
- Orange = 2.1 to 2.2 volt.
- Yellow = 2.1 to 2.4 volt.
- Green = 2 to 3.5 volt.
- Blue = 3.5 to 3.8 volt.
- White = 3.6 volt.
Then using Ohm’s law, the appropriate resistance R can be calculated for the voltage of the source V source that we use. The term I, in the formula, refers to the current value for the light intensity we need. The common is 10 mA for low luminosity LEDs and 20 mA for high luminosity LEDs; a higher value can disable the LED or considerably reduce its lifetime.
Other LEDs with a higher current capacity known as power LEDs (1 W, 3 W, 5 W, etc.), can be used at 150 mA, 350 mA, 750 mA or even at 1000 mA depending on the opto- given by the manufacturer.
It should be remembered that several can also be connected in series, adding the potential differences in each one. Parallel configurations can also be made, although these types of configurations are not highly recommended for efficient LED circuit designs.
For the calculation of the resistance value, Ohm’s Law must be taken into account, in the example, this type of battery is 9 volts, and the led diode needs 1.8 volts, so they have to fall into the resistance the difference is 7.2 V and the consumption of the diode is about 18 mA (0.018 A), therefore 7.2 / 0.018 = 400 ohms.
Basic parallel connection diagram.