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 degree Kelvin (K) is the unit used to classify the color temperature according to the scale created by William Thomsom from degrees Celsius. Lord Kelvin based on the table of William constructed a scale of temperatures to which its name is attributed to him.
A deeper explanation would introduce us into the world of physics, so in our sector knowing the relationship between Kelvins and kind of light will be sufficient.and.
This measurement factor is useful to know at a glance which tone or quality of light has a certain light source, for example, if we are going to buy a light bulb or a fluorescent we may be interested in knowing the kelvin it provides, as it will depend on This factor whether the light will be yellow or white.
The lower the kelvin value will be the light temperature, for example a 1600K bulb will have a temperatUra and color quality similar to the light of an exit or sunset. While a light bulb with 5000K will be more like daylight.
To better understand the relationship between kelvin and light temperature is attached the following table, where in a visual way it becomes easier to choose the type of bulb that best suits our needs.

A: It is equivalent to the temperature of a candle, it is aIn yellow light.

B: It resembles the color of dawn, it is similar to a tungsten bulb.

C: It is the tone of light of the old bulbs that were not led, filament bulb.

D: Similar to a study light.

E: Similar to mid-afternoon light about 20 °, similar to a fluorescent light warm.

F: Similar to mid-afternoon light at about 30 °.

G: Daylight, similar to a lightOf a flash.

H: Sunlight at noon.

I: Very sunny day and clear sky.

J: Partly cloudy day.

K: Cloudy day.

L: Wide shade clear day.

M: Very cloudy day.

N: Blue sky without sun.

O: Very clear day.

The lumen (symbol: lm) is the unit of the International System of Units to measure the luminous flux, a measure of the light power emitted by the source. The luminous flux of radiant flux difference that the former provides the variable sensitivity of the eye to different wavelengths of light and the latter involves all electromagnetic radiation emitted by the source according Wien law and Stefan-Boltzmann regardless of whether such radiation is visible or not. 1 lm = 1 cd. sr = 1 lx. m2