Alternative Technologies for the High Pressure Sodium lamps (HPS)

Today most fluorescent lamps are regulated by the RoHS Directive. However, despite containing mercury, there are still exemptions. In the field of general illumination, High Pressure Sodium lamps (hereinafter abbreviated as HPS) remain the highest runner of mercury-containing lamps.

HPS is typically used in street lighting luminaires, classified under item 4(c) and for horticulture classified under item 4(f). They are exempt until at least February 24, 2027, due to the lack of alternative technologies. However, Nichia considers that the hurdles for alternative technologies, including commercial elements, have already disappeared through the remarkable development of LEDs in recent years and there is no need to extend the exemption. Below, Nichia will look at the current status and future possibilities of replacing HPS with LED technology, within street lighting and horticulture markets respectively.

As the satellite image clearly shows, the most widely used outdoor light source in the world is HPS, which emit the nostalgic color of gaslight lamps. Examples include container yards glowing with the color of gaslights and cobblestone streets throughout Europe with street lighting aimed to retain the atmosphere of the medieval times.

Even with the rapid shift to LED lighting and the replacement of most conventional light sources such as fluorescent and incandescent lamps with LEDs, HPS is still extensively used because of their relatively high efficiency and long life amongst conventional light sources. That being said, it is hard to beat the rapid technological evolution of LEDs, especially for new street lighting, which is rapidly switching to LEDs. On the other hand, in familiar places such as old residential areas, parks, and city street lighting, there is a strong opposition to replacing the nostalgic color of gaslight lamps with the cooler white light of LEDs. In addition, recently attention has been drawn to so-called "light pollution" from the bluish white light of LEDs. The shift to LEDs in this market is a seesaw battle. Nichia's "HPS color LEDs" released in 2021 have the potential to change this situation and accelerate the shift to LEDs, which also contributes to the realization of a mercury-free society.

LED Lighting has already been widely adopted in closed-type indoor artificial farms where vegetables and fruits are grown. However, many HPS are still used today in greenhouses where natural sunlight is used as the basic light source in addition to supplements of artificial light on cloudy days, evenings and nights. This is also due to the relatively high efficiency and long lifetime of HPS vs. conventional light sources. In recent years though, LEDs have been used in most newly constructed green houses. Lately, LEDs have surpassed HPS in both efficiency and lifetime, and LEDs are able to adjust their color and spectrum to suit plant growth in a way that is not possible with HPS. It is believed that LEDs can increase the amount of a harvest, speed up the growth and the harvest season, and also improve the taste and nutritional value of vegetables and fruits in the future. In addition, HPS have disadvantages, including a high heat radiation which increases the cost of air conditioning and requires a large facility to keep a distance; HPS LEDs have significant advantages in these respects as well. Because of the various advantages of LEDs, it is becoming commonplace to use LEDs for newly constructed facilities, although there is a somewhat high economic hurdle to replace existing HPS with LED lighting, including the power supply and other components. The field of horticulture is constantly advancing, and a variety of LEDs have appeared on the market, including Blue/Red combinations, white, white and red, and so on. Through many experiments in its own vertical farm, Nichia has succeeded in commercializing "Hortisolis”, the most suitable LED with the ideal spectrum for plant growth. Since its launch, this LED have been highly evaluated. Whether Nichia's "Hortisolis™” will retain its "best/optimum” status in the future, or whether something better will come along, nobody knows, but Nichia believes that at least it can be said that LEDs have already established themselves as an excellent alternative technology to HPS.

While HPS for general lighting are still widely used today, LEDs have already established themselves as an alternative technology that can be used, both technically and commercially. Nichia will make further efforts to continue rapid introduction of LEDs, and the RoHS exemption will end on February 24, 2027, to ensure the realization of a mercury-free in lighting filed.