High pressure sodium lamps. Sodium lamps for plants in greenhouses
Discharge sodium lamps are the most efficient among existing light sources in terms of the ratio of light output to the energy expended, but their spectrum is uncomfortable for the human eye. The absence of blue color forms a monochrome picture of the surrounding space. Because of this feature, sodium lamps, despite their excellent economy, are used on a limited basis - mainly for street lighting. Meanwhile, the predominance of the yellow-red "solar" and green spectra has a beneficial effect on the growth of all plant species, which has found wide application in greenhouses.
What is sodium lamp
They belong to gas-discharge lamps by analogy with mercury, fluorescent, halogen, xenon "brothers". The source of luminescence is sodium gas in combination with other elements, pumped into a glass flask.Under the influence of an electric arc, sodium is heated to high temperatures and begins to glow bright yellow-orange light, turning into a red spectrum by the end of the lamp life.
The power of sodium lamps is the highest in the class - up to 200 Lm / W (Lumen per Watt). Characteristic features are the low color temperature (2100-2700 K) and the dominance of the yellow-red emission spectrum with a minimum amount of blue. This combination leads to the fact that lamps of this type fill the surrounding space with monochrome yellow-orange light, as a result of which the human eye does not sufficiently distinguish colors and outlines of objects. They lose depth, volume, orientation and assessment of distances to objects is hampered. But for plants at certain stages of growth just need a "solar" radiation spectrum.
Types of lamps
By the principle of work, they are divided into two main classes:
- High Pressure Sodium Lamp (HPS - HighPressure Sodium).
- Low Pressure Sodium Lamps (LPS - Low-Pressure Sodium).
Developed LPS-lamps in the 30s of the last century. They have the highest efficiency (180-200 Lm / W), however, due to constructive imperfections, these lamps turned out to be capricious and even dangerous.Normal quartz glass is defenseless against the aggressive effects of sodium: it quickly evaporated, and if the lighting device is broken, the gas may explode (ignite) when it reacts with oxygen.
In the 60s, General Electric developed ceramics using aluminum oxide (polycore, lukalos) that can withstand sodium at high temperatures. This breakthrough made it possible to return to the production of this type of lighting devices with excellent economy. To improve the glow of the gas it is pumped under high pressure. The circuitry is simpler than that of LPS. Unfortunately, the increase in gas pressure and other factors led to a significant decrease in light output - up to 50-150 Lm / W (depending on its power), but the color rendering ratio (CRI) increased from 20 to 85 and higher (from insufficient to good) .
Lamps with low-pressure sodium lamps in the world are not widely spread. In the USSR and the USA, they bet on more technological mercury lighting systems. In a number of European countries they are actively used for road lighting.
High pressure sodium lamps are more common.We use them to illuminate city streets, in landscape design, to highlight architectural objects. They are used in industrial premises where bright light is not required. Recently, leading corporations (Philips, General Electric and others) have significantly improved the design and consumer qualities of these lamps: their spectral coverage has increased significantly, the color temperature has increased (from 2100 to 2700 K) - some models are already suitable for lighting residential (production) premises . Of particular note is the use of sodium lamps in greenhouses.
Sodium lamps differ in several important ways. By constructive type, they are divided into:
- Arc sodium mirror (DNAZ).
- Arc sodium matted (DNaMT).
- Sodium arc in a light-diffusing flask (DNaC).
- Arc Sodium Tubular (DNaT).
Also distinguish the lamps on the current consumption (220V and 380V), which, in turn, are divided by power: from 50 to 1000 watts.
Sodium lamps for greenhouses
Analysis of the energy consumption of greenhouses showed that the most energy-intensive processes are the irradiation and heating of plants. About 40% of the electricity consumed by greenhouses is used for irradiation.Therefore, farmers achieve an increase in vegetable production due to the introduction of energy-saving lighting devices.
Of great importance, in addition to the optimal parameters of the greenhouse microclimate, is the quality of irradiation of plants. Therefore, it is also relevant to study the effect of qualitative lighting parameters on the growth and morphological development of seedlings. The use of fundamentally new light sources in plant irradiation technologies — modern sodium luminaires in combination with other light sources (for example, LEDs) —- makes it possible to significantly increase the final yield.
The leader in the improvement of greenhouse lighting is the Dutch corporation Philips, which is not surprising, given the leading position of the greenhouse industry in the Netherlands. The company conducted research studies (in 2012 in Ukraine, in 2013 in Holland), which proved that sodium lamps are the most preferable for plants. They are more efficient than compact fluorescent lamps with less luminous efficacy and not providing the optimal light spectrum.In parallel, it has been proven: incandescent lamps and mercury lamps consume too much electricity to be cost-effective.
Even better results are achieved if the plants are illuminated not only from above, but also on the sides, between the rows. For this, economical LEDs are quite suitable. The combination of sodium lamps with LEDs contribute to higher yields. In 2012, the first industrial greenhouse was created in Uman (Ukraine), where these types of lighting devices were combined. The area of the site with mixed lighting SD and sodium lamps was 6000 m2. A total of 1230 LED modules and 870 fixtures with DNaT lamps were installed in the greenhouse. The experiment showed that the yield of tomatoes (subject to other requirements) can reach 73 kg / m2annually.
Then, thanks to a similar experiment in the Netherlands (2013), the joint use of HPS and DM resulted in an increase in yield by 30%. In the future, the technology was adopted in England, Denmark, Canada, Japan, China and other countries.
As a rule, industrial greenhouses are made of transparent materials so that the plants are illuminated by the sun.However, at latitudes more than 40about(closer to the poles) natural lighting is only enough for 4-5 months (May-September). Additional time is needed in the remaining time. Moreover, at different stages of the growing season and for different crops requires its own spectrum of radiation.
The luminaire under the sodium lamp is placed on top - it charges the plants with yellow-red "sunlight" (the green spectrum, also emitted by these lighting devices, is not so important). Light-emitting diodes (or fluorescent lamps) are advisable to use as an additional tool for lateral irradiation, the main advantage of which is that, being in the lower part of a vertically grown plant, the light falls on the lower tiers of the leaves, which do not receive enough high light. This combination increases the intensity of photosynthesis, promotes growth, proper development of plants. Additional lighting is useful at the stages when the grown crops require a blue spectrum of light, which is almost absent in sodium lamps.
How it works
For the absorption of photons of light in plants, special pigments are responsible - carotenoids, a- and b-chlorophylls. Caratinoids absorb light exclusively in the blue range, chlorophylls in blue and red.However, the absorption maxima of chlorophylls - the main photosynthetic pigments - are within 640-680 nm, and the carotenoids - within 470-480 nm. According to these parameters, high-pressure sodium lighting lamps (NLVT) with an operating range of 500-700 nm are considered the most efficient light sources for greenhouse conditions. Their stability, term of work, light return, economic efficiency are the most optimal.
Lamps with a power of 50-150 W are less reliable and have a low stability of parameters during the service life than lamps of average power (250 W and more). The reasons for this are in the presence of a noticeable rectifying effect in the event of ignition of low-power lamps, which can reach 2 minutes. At the same time, an increased current passes through the lamp, resulting in intensive sputtering of cathode materials and the formation of an opaque film on the inner surface of the discharge tube. The ignition pulse and the magnitude of the starting current affect the significance of the effect of rectification, so the pulse energy must provide a quick transition from a glow discharge to an arc. To prevent the effect of current rectification, devices are used to block DC current.Therefore, in greenhouses often use NLVD power from 250 watts.
However, numerous theoretical and experimental studies of the processes in the discharge, on the electrodes and in the near-electrode areas of gas-discharge lamps have shown that there are a number of issues that require further improvement. For NLVT, which are used in crop production of closed soils, it is necessary first of all to optimize the spectral composition of radiation for specific light cultures and to reduce the content of mercury in the discharge tube, preventing possible environmental pollution by mercury vapor from devices that have failed.
The creation of modern technologies for growing greenhouse plants is associated with the use of high-intensity discharge lamps, in particular sodium. Their widespread use is a positive factor in the intensification of this production, although it is associated with a serious environmental problem. The composition of the vast majority of modern discharge lamps include a toxic substance - mercury. Sodium lamps, for example, may contain sodium amalgam (an alloy of mercury).If such a lamp breaks above the plantings inside the greenhouse, plants placed under it (greens, vegetables, seedlings, indoor flowers) become unsuitable for use.
The main direction of improving environmental performance is the creation of highly efficient mercury-free discharge lamps. Recently, these works were carried out by individual lighting companies, including in the CIS countries. Sodium lamps with a reduced amount of mercury in the discharge tube and fully mercury-free models already exist and are increasingly used in greenhouses.