VAC would be the abbreviation of Volt Altern Current which would be translated Volts of alternating current. The difference between VDC is that its sinusoidal oscillation achieving a more efficient energy transmission.

The alternating current is the energy that we receive in our homes, it is generated in the power plants by means of alternators.

The intensity of this type of current varies with time, and changes direction 50 times throughsecond (50hz). The generated voltage changes in the form of sine wave so it is not constant.

In the image:

1. Current by pulsations.
2. Direct current (DC).
3. Alternating current (AC).
4. Variable current.

The SMD LED is an LED module that uses a surface mount technology to place a diode on the surface of a printed circuit and encapsulated on a semi-rigid resin. Typically used for lighting all types, since its opening angle can be 360° and LEDs, being very small, they can be distributed throughout the bulb. Ideal for decoration lighting in homes or places of transit dondand they will not be on continuously. It is also often used in automotive interior lighting. Each LED SMD chip is identified by a 4-digit number. This code identifies the size of the LED chip, the first two digits indicate the height and width the next two, in millimeters. For example, the dimensions of a LED 5050SMD are 5.0 x 5.0 mm. There is an exception, 3528SMD LED chip is also knownon how 1210SMD, with dimensions 3.5 x 2.8 mm.

Surface mount technology, better known by its acronym SMD (Surface Mount Device) is the method of construction of electronic devices most currently used. It is used for both active and passive components, and is based on the assembly thereof SMC (Surface Mount Component English) on the surface of the printed circuit. In the case of SMD LED technology is the differently constructedon the plate makes SMD LED and have a physical difference.