How to Improve the Light Efficiency of Plant Lights？

Since the HID era, plant lighting has not been a new type of lighting application. However, LED lights can customize different spectra for different plants. Its usage and iterations have completely updated the entire plant lighting industry, thus making the plant lighting market one of the fastest-growing markets globally, especially in the United States and Europe. This article provides some ideas on how to improve the lighting effect of plant lights and create better plant lamps.

1、The influence of light on growth 
In the natural spectrum, the effects of different wavelengths of light on plant growth are as follows: 
a) The wavelengths ranging from 280 to 315 nm have very little effect on the morphology and physiological processes. 
b) 315 - 400 nm wavelength range, chlorophyll absorbs less light, which affects the photoperiodic effect and thereby hinders the elongation of the stem; 
c) 400 - 520nm (blue light), the absorption rate of chlorophyll is the highest, promoting photosynthesis; 
d) 520 - 610 nm wavelength range, with low pigment absorption rate, leads to a decrease in photosynthesis. 
e) 610 - 720 nm (red light), with a low absorption rate of chlorophyll, significantly affecting photosynthesis and photoperiod. 
f) 720 - 1000nm, low absorption rate, stimulates cell elongation, affects flowering and seed germination; 
> 1000 nm is converted into heat. 
 

Generally speaking, PAR (Photosynthetically Active Radiation) refers to the spectrum that can effectively stimulate photosynthesis in plants, with a wavelength range of 400 to 700 nanometers.

2. Several concepts regarding how plant lights can be more efficient 
 

a) The efficacy of a plant lamp refers to the efficiency of a plant lighting system in converting electrical energy into photons (PAR) that can be used for photosynthesis. Many plant lamp manufacturers use the total wattage or the wattage per square foot as the measurement standard for light intensity. However, these values do not provide any information because watts are a measure of electrical input rather than light output. If the PPF of the light and the input power are known, the efficiency of the plant lighting system in converting electrical energy into PAR photons can be calculated. Please note that the unit of PPF is μmol/s, while the unit of electrical energy is joules per second (J/s). Therefore, the seconds cancel out and the unit becomes µmol/J. The higher the value, the higher the efficiency of the lighting system in converting electrical energy into PAR photons. 

b) PPF refers to the photon flux of photosynthesis. PPF measures the total amount of PAR generated by the lighting system per second. It is measured using a specialized instrument called an integrating sphere, which can capture and measure all the photons emitted by the lighting system. The unit of PPF is micromoles per second (μmol/s), which is probably the second most important method for measuring a plant lighting system, but for whatever reason, most lighting companies do not list this indicator. It is worth noting that PPF does not tell you exactly how much light is actually falling on the plants, but if you want to calculate the efficiency of the lighting system in generating PAR, it is an important indicator. 

c) PPFD refers to the photon flux density for photosynthesis. PPFD measures the total amount of PAR that actually falls on the plants, or as scientists put it: "The number of photons per second that promote photosynthesis on a given area." PPFD is a "point" measurement of a specific location on the plant canopy, with the unit being micromoles per square meter per second (μmol/m2/s). If you want to know the actual luminous intensity of a specified growth area (for example, 4'x 4'), it is very important to take the average of several PPFD measurements at a certain height. Some lighting companies only publish the PPFD values measured at the central point of the coverage area, which greatly overestimates the actual luminous intensity of the lamps. A single measurement value does not represent anything because usually the center of the lamp is the brightest, and the closer you measure towards the edge of the coverage area, the weaker the luminous intensity becomes.

 
When light propagates from the source to the destination (from the plant light to the plants), it weakens. You will notice in most growth light intensity charts that the PPFD value decreases as the distance increases. 

This is why it is important to pay attention to the height at which the plant lights are hung when planting.

In order to select the appropriate plant lighting system to meet the planting and business goals, it is necessary to understand PPF, PPFD and luminous efficacy in order to make a wise purchasing decision. However, these three indicators cannot be regarded as the sole factors for making the purchase decision. Other factors such as size and utilization rate also need to be considered.

All factors need to be taken into consideration to select the most suitable system based on your farming and business goals. The message to convey is that PPF, PPFD and light efficiency are the parameter standards used by scientists and leading plant lighting companies in the industry. If a company does not provide you with these parameters for plant lighting, then they should not be sold, and we cannot verify whether their system is effective.

3. Select the appropriate LED power supply to enhance the performance of the lighting fixtures. 
a) Select the appropriate power for the lamps.

Different plants will respond differently to PPFD.

b) Select the appropriate input voltage for the lamps. 

There are mainly two different input voltage ranges: 120-277Vac and 200-480Vac, which can cover most plant light applications. As the power range increases and the cost of wire materials rises, more and more users choose high-voltage input to reduce power loss of the wires and the cost of the wires. 

c) An efficient power supply means higher light output and a longer service life. 

The high-power power supplies from first-line power supply manufacturers (such as 600-800W) have an efficiency of over 95%, while those with 300-400W have an efficiency of 94%. In high-power applications, a 1% difference in efficiency means a difference of over 10% in heat dissipation, which leads to a temperature difference of 10-20 degrees among the internal components. As is well known, for every 10-degree decrease in capacitor temperature, the lifespan of the power supply will be doubled, and it will also bring about better MTBF. 
 

d) Should a single high-power power supply or multiple low-power power supplies be chosen? 

For high-performance power supplies, a single high-power supply should be the preferred option. The reasons are as follows: 
- Higher efficiency. The more small-power power supplies are used, the higher the power loss and the lower the efficiency. 
- The wiring is simple. The failure rate doubles or triples. The more power supplies there are, the higher the failure rate becomes, and the more difficult it is to maintain. 
- Surge current. When multiple power sources are operating simultaneously, it will result in a higher surge current. 
- Inconsistent startup. Multiple power sources have different startup times, resulting in poor user experience. 
- Higher dimming drive current. Usually, a single lamp controller can drive at least 50 power supplies. Therefore, the more power supplies there are in a single lamp, the fewer lamps can be controlled. Moreover, a larger number of power supplies in the control circuit will result in higher voltage drop on the dimming line, which may cause inconsistent brightness of different lamps.