Voltage and current for grow lights 101
All you need to know about electricity when it comes to powering your grow light
Voltage and current
In a circuit electricity is measured using the following units : Volt (V) and Ampere (A).
Volt is defined as a difference of potential between two points in a circuits : it means the amount of energy needed to move one given electric charge between two points. It measures the Voltage (U) of a circuit
Ampere is defined as a quantity of charges going through a given point in the circuit per unit of time. It measures the current (I) flowing through a circuit.
Electricity circuits can be seen as water pipes. The pressure (ie the force) of the water inside the pipe is its “voltage” and the quantity of water flowing through it is its “current”
The led U-I curve
Leds and COBs (which are just lots of small leds in the same component) impose a strict relationship between the voltage (U) and the current (I) in a electricity. This behavior is described by the U-I curve of the component which read as follows :
Zone 1 : Blocking zone : The led blocks the current because voltage is not enough. No electricity go through the led, it is off. The led stay in this state if voltage applied to the led is below its forward voltage (Vf). Between the + and - terminals of the led the current is 0 when the Voltage is below Vf.
Zone 2 : Passing zone : The led let the current go through it because the voltage applied to it is above Vf, it is on. It will let any current flow trough it between 0 A and its Max admissible current (Imax). Between the + and - terminals when the current is passing the voltage is always equal to Vf.
As all leds behave following similar curves, manufacturer usual describe their product by specifying :
The forward Voltage (Vf) : The voltage that needs to be applied to the led to light it up.
The Absolute maximum current (Imax) : The maximum current that can go through the led without risking damaging the led
The nominal current (Inom) : The current at which the led is tested (spectrum, efficiency, power consumption ect…)
Driving led grow lights
Leds are components that impose a fixed Voltage value (Vf) while the current in the circuit can be anything between 0 and Imax. This is why they are powered using constant current (CC) power supplies. These power supplies send a specified current into the circuit and match their voltage output to the circuit needs. They are specified by their :
Current output or Rated current : The current they will push into the circuit, this value will be imposed to the circuit by the power supply.
Voltage Output or Constant current region : The Range of voltage at which the power supply can operate. This value is fixed by the circuit and the power supply will adapt to it.