LED Growth Lights VS HPS Lights(high-pressure sodium Light)

Vegetables are indispensable for diet, With the vegetables demand increasing, greenhouse cultivation is becoming more and more popular.Therefore,insufficient sunlight in the greenhouse has also become a problem in the growth of plants.

On the other hand, it is the insufficient light of the greenhouse crops caused by climate change, such as winter or rainy weather etc. So, the plant growth lights are more and more popular.

Plant growth light is beneficial for applying a series of growth problems,such as metal halide light, high-pressure sodium light and LED plant growth light have been or are being used in greenhouse lighting. Among these types of light sources, high-pressure sodium lights have higher luminous efficiency, longer service life, and higher overall energy efficiency, occupying many share in the past, but the high-pressure sodium lights have poor lighting sustainability and  unable to illuminate at close range are disadvantages. However, LEDs are more expensive, Why?So what is the difference between LED plant growth lights and high-pressure sodium lights.

First of all, let’s look at the difference between high-pressure sodium  and LEDs.

The difference of light-emitting principle and external structure

The high-pressure sodium light is composed of mercury, sodium, xenon arc tube wick, glass bulb, light, etc. Since the difference of ballasts,there have inductance high pressure sodium light and electronic high pressure sodium light.  LED is also called light-emitting diode. The core part is a wafer composed of P-type semiconductor and N-type semiconductor. There is a transition layer between P-type semiconductor and N-type semiconductor, which is called P-N joint, When the current flows from the positive to the negative, the semiconductor will emit light of different colors from UV to red, and the intensity of the light is related to the current,such as normal brightness (luminous <10mcd), high brightness (luminous 10-100mcd) and very high brightness (luminous > 100mcd).

The difference of the irradiation and spectral range

The light-emitting angle of the high-pressure sodium light tube is 360°, and most of them comes with a reflector before illuminate the targeted area. The spectral energy distribution is about red-orange light, yellow-green light, and blue-violet light . According to the different light distribution design of LED, its effective light-emitting angle include: ≤180°, 180°~300° and ≥300°. The wavelength of  LED light source adjustable and can emit monochromatic light with a narrow light wave, such as infrared, red, orange, yellow, green, blue, etc., which can be combined arbitrarily according to needs.

The differences application and lifespan

The high-pressure sodium light has a wide range application, high luminous efficiency, strong penetrating ability, and high life span of 24000h advantages, However,When the sodium light work, it will produce a lot of heat, so it is a kind of heat light source. there is also a problem of self-failure in the work,. LEDs is driven by DC, lifespan more than 50,000 hours and low attenuation. As a cold light source, it can be close to plants. Moreover,LEDs does not contain harmful elements, and is more environmentally friendly.

A large number of scientific research show that plants lights can not only increase crop output and shorten the planting cycle, but also effectively improve crop quality,Both the use of high-pressure sodium light and LEDs are good to promote the plants growth, But they have some difference.

Output and quality differences

The high output and high quality of crops is the goal of planting and cultivation. LEDs can improve the output and quality of pepper, tomato and eggplant seedlings etc,LED can also improve the quality of grape . Among them, applying the blue light is more fast, the single-grain quality is higher, and the sugar content is high. The ultraviolet light is beneficial for improving single-grain quality during the ripe period.

Similarly, the 70W high-pressure sodium light is beneficial for increasing the yield of strawberries per plant,(increasing 17.9%). High-pressure sodium light and LED both have a significant impact on the morphology of plants.

Differences Appearance

The plant appearance is an important index in the process of plant growth, especially for seedlings, which determines whether healthy plant growth. In general, the seedlings of conifer plants grown under LED growth light better than high-pressure sodium light.

In 12 hours lighting, density 50μmol/(m2·s), LED red light (630~660nm), orange light (590~610nm), blue light (450~460nm), green light (520~540nm) condition,compared with natural light [120μmol/(m2·s)],,it will significantly increase the seedling index of tomato.

After using LED growth lights, the plant height, stem thickness, and leaf area of pepper, tomato and eggplant seedlings increased significantly.Moreover, the weight per unit area of the upper, middle, and lower leaves of the tomato are also increased significantly.

In 61±2μmol/(m2·s) HPS, natural light, and 3 different proportions of LEDs condition,the tomato leaf area and leaf number under 95% red light + 5% blue LED is higher than the HPS in the early stage. The plant height, stem thickness and leaf area of ​grafted watermelon seedlings is better than that of HPS. These results all show that the growth status of plant leaves is higher than that of HPS.

However, the stem elongation and leaf area of rose under LED are low, and there is no much difference in dry weight and fresh weight between several plant experience,also suitable for pepper, tomato, geranium, petunia.

The height, number of leaves, fresh weight and dry weight of tomato seedlings under the 200μmol/(m2·s) HPS are greater than the LED. Moreover, the fresh weight of tomato plants under alternating LED and HPS lights is lower than that of HPS lights alone. Under the HPS lights,the leaf transmittance and reflectance of leaves are higher, which also allows light to reach the canopy better. After a series of comparisons, the LED plant growth light ratio, temperature, and light density have a significant relationship to plant growth.

Physiological differences

The content of chlorophyll directly affects the photosynthetic action. The gas exchange rate and chlorophyll content of conifer seedlings grown under LED are higher than that of HPS lights.

In the eight growth experiments conducted by FINE PIXEL, the average photosynthetic pigment content (per unit leaf area) of 5 plants grown under LED higher than that of HPS lights.

The content of chlorophyll A and chlorophyll B of tomato seedlings with a combination of 200μmol/(m2·s) red and blue LED plant growth light is greater than that of HPS lights under the same light density.

Carotenoids are another element in photosynthesis of chloroplasts,which can protect chlorophyll from damage by strong light.

Research shows that using HPS lights will increase the concentration of carotenoids and nitrates in lettuce. The soluble sugar, carotenoid and nitrogen content in the seedling leaves of pepper, tomato and eggplant under LED will be increased.

When the plants were growing with HPS and LED (RB, RW) lighting, the water use efficiency of tomatoes and eustoma under HPS is higher than that of LED, and the transpiration rate is lower than that of LED t. There is no difference between the CO2 exchange rate.

In addition, LED(R:FR=3.09)500μmol/(m2·s) will significantly affect the flowering time and flowering rate of lentils. Both LEDs and HPS will increase the content of photosynthetic pigments, However, the accumulation of photosynthetic pigments and the transpiration rate under LEDs is higher than that of HPS.

The special spectral ratio of LEDs can also affect the flowering of certain plants.

The difference cost of high-pressure sodium and LEDs

Compared with traditional light sources, HPS and LEDs have obvious advantages.At the same output, the LED only needs to consume 75% of the energy, however,under the condition of the same efficiency output , the initial cost of LEDs is 5-10 times that of HPS lights.

For flowerbed plants, 150W HPS lights and 14W LEDs can achieve the same effect, So,LED will reduce electricity bill.

Wrapping up

Green plants absorb much of red-orange light with wavelength of 600-700nm and blue-violet light with wavelength of 400-500nm, and only a small amount of green light with wavelength of 500-600nm absorbed. Both high-pressure sodium light and LEDs are good for plants.  

High-pressure sodium light are cheaper than LEDs, However, high-pressure sodium lights need to come with ballasts that increases use costs.

Compared with high-pressure sodium light, LED technology has great potential in improving plant growth,LEDs have narrower spectral adjustable, high reliability and high flexibility in the application.

In terms of crop yield, LED has no obvious advantage over high-pressure sodium light.So,we should make a reasonable selection according to actual conditions,if you are interested in more LEDs,here more about Quantum board vs COB LED growth lights.