# Units of measure

• ## Ampere (A)

Basic International System unit of measure for the intensity of an electrical current; it refers to a real power consumption. The measurement is the relationship between wattage and voltage (A= W/V).

## Candela (cd)

The base unit in the International System of Units referring to luminous intensity, that is, the light concentration/ power emitted by a light source in a particular direction on a solid angle (steradian). This value is irrespective of the distance at which it is measured. Candelas are calculated from lumens according to the following formula: 1 lm/sr (lumen by steradian) = 1 cd. Usually the luminous intensity of dichroic bulbs is indicated in candela specifically because it is directed in a particular light cone.

## Hertz (Hz)

Unit of measure for electrical frequency indicating how many times an event occurs within a second.

## Kelvin (K)

International System unit of measure for temperature; in lighting design it refers to the colour tone of the light emitted. The LEDs we use are generally warm white (average 2,700 K).

## Lumen (lm)

Unit of measure that corresponds to the photometric equivalent of a watt. It refers to the luminous lux (in other words the quantity of luminous energy emitted by a light source) visible by the human eye. In general, what relates the intensity with the lux (candela with lumen) is the angle of emission of light. To calculate the lumen/ candela conversion, you have to convert the radiation angle of the beam (supplied by the manufacturer in degrees) in a solid angle (unit of measure: steradians). Thus we can calculate, for instance, that a LED with an intensity of 2.4 cd and a diffusion angle of 120 ° will present a lux of about 7.5 lm.

## Lux (lx)

Unit of measure for illuminance of the luminous ux (lumen) per unit area. In other words, it indicates the visible lux (lumen) per square metre at a particular distance. The greater the distance between the source and the surface, the lower the lux detected.

## Volt (V)

Derived unit of power in the International System of Units for the measurement of difference in potential; it usually refers to the voltage of the electrical system (230V, 110V, 12V, 24V) or to the supply voltage of the light sources.

## Watt (W)

Unit of measure of the International System of Units referring to electrical power (W = V * A) and so to actual consumption. For instance: a LED board with a voltage of 2.85 volts powered at 350 mA consumes about 1W.