The most common LED type used to generate white light involves coating LEDs of one color (mostly blue LEDs made of InGaN) with phosphor to form white light. These LEDs are called phosphor-based white LEDs. The “blue” photons emitted by High-brightness LED either passes through the phosphor layer without alteration, or they are converted to the “yellow” photons in the phosphor layer . The combination of “blue” and “yellow” photons leads to white light.
The “blue” photons emitted by High-brightness LED Grow Lights either passes through the phosphor layer without alteration, or they are converted to the “yellow” photons in the phosphor layer . The combination of “blue” and “yellow” photons leads to white light.
White LEDs – Colour temperature
Color temperature or CCT of a light source is the temperature of an ideal black-body radiator (solid object with certain properties heated up to point of incandescence) that radiates light of comparable hue to that of the light source, and its temperature is expressed in Kelvins (K). As a black body gets hotter, wavelength of light emits progress through a sequence of colors from red to blue.
Increasing the quantity of phosphor coating on the blue led leads to more phosphorescence and increased the ‘yellow’ to blue ratio. This results in a ‘warmer’ or more orange light with a lower correlated color temperature (CCT) of 3000K.
Decreasing the phosphor coating has the opposite effect and the proportion of blue photons emitted is greater and the light is a ‘cooler’ light spectrum with a lower correlated color temperature (CCT) of 5000K.
Higher CRI white LEDs ‘smoothen’ the spectrum curve so that there is a more even spread of wavelengths across the PAR range. However it does not increase the Photosynthetic efficiency of the light spectrum.
Deep red LEDs
Although more expensive per watt the deep red LEDs of about wavelength 660nm are very electrically efficient and are added to grow lights to increase the system efficiency.
Typically a small number of 660nm reds are used in most full spectrum LED grow lights and the spike at this wavelength is visible on the grow light spectrum graph
UVA and Far red LEDs
Some grow lights will also include UVA LEDs at about 380nm and Far Red LEDs of wavelength 730nm. These are not in the standard PAR range so the additional UVA or Far red light is not sensed with a PAR sensor. However these wavelengths do generate photosynthesis and contribute to growth and yield.
To power LEDs, you need a device that can transfer the mains AC power supply to DC – otherwise known as an LED driver. This is because LEDs are designed to run on direct current (DC) while mains power is Alternating Current (AC).
The LED driver will also provide electrical protection to the LEDs to prevent damage by power surges, over heating etc.
There are type main types of LED driver:
Constant Current (CC) – LEDs are mostly in serial connections and the LED driver delivers a precise current value. Ideal for dimming.
Constant Voltage (CV) – LEds are mostly in parallel connection, ideal for decorative strips which can be cut to the required length. Not recommended for dimming.
LED Grow Light driver characteristics
Rated Current/Voltage – predefined output current or voltage to service the number of LEDs it will power and how hard they will be driven.
Rated Power – Output power of the driver. Output Voltage x Amps = rated power
Efficiency – The ratio between the output power and input power in %.
Higher quality drivers tend to be higher efficiency, run cooler and last longer.
LED driver efficiency
LED drivers will range from about 80% to 95% efficiency. The efficiency is a measurement of the power output/power input and indicates how much power will be lost. For example a 90% efficiency driver loses 10% of the power it consumes to heat. To have an efficient and effective grow light it must have a good LED driver with high efficiency. An LED driver is considered efficient if it is 90% efficient or greater.
LED driver reliability
The most common failure of an LED light is not the LEDs themselves but the LED driver. The drivers tend to fail due to high operating temperatures which dry out the capacitors in the circuits and the driver will stop working. A good quality and high efficiency LED driver is necessary for a grow light to be reliable.
There are two main methods of dimming LED lights: Pulse Width Modulation (PWM) and analogue.
PWM: Unlike traditional lighting such as incandescent, this method of LED dimming doesn’t rely on voltage to influence the level of brightness. Instead, an ‘on and off’ cycle is used. This cycle operates in a matter of milliseconds, so to the naked eye, you won’t actually notice them turning on and off.
For instance, if you have dimmed your lights to 30%, they will cycle ‘on’ for 30% of the time and ‘off’ for the remaining 70%. This creates an optimal dimming effect without having to increase or decrease voltage reaching the light.
Analogue: A more straight forward approach to dimming. Analogue relies on controlling the current to either dim or brighten the lights. Lowering the current will dim the lights, and at the opposite end, increasing the current will create a brighter light.
Other LED driver functions
Most good LED drivers will also have other safety features such as:
- Overcurrent protection
- Overtemperature protection
- Short circuit protection