Street lighting: DRL lights or LED floodlights

Recommendation points

• An excursion into the theory of lighting engineering
• The principle of operation of LED, DNaT and DRL
• The issue of size and ease of placement
• Light parameters of different sources
• Maintainability, safety, disposal

Making the right choice of light sources is not easy. To illuminate outdoor areas and home gardens, you need reliable, durable and economical lighting technology. We offer to understand the strengths and weaknesses of different sources of street lighting.

An excursion into the theory of lighting engineering

We are so accustomed to electric lighting that we consider it quite natural without going into the technical details. Meanwhile, almost everyone knows the feeling of insufficient illumination, although the light source is powerful enough and literally blinds the eyes..

The reason for this phenomenon lies at the intersection of the physical characteristics of the light flux and the principles of light perception by the human eye. The so-called spatial angle of visible radiation (scattering) is the wider, the larger the size of the luminous body.

Luminescent tubes, like the bulbs of DRL lamps, emit with their entire surface, so the feeling is created that the space is flooded with light. In contrast, LEDs are tiny. Such a luminous point creates a sharp difference in brightness: planes located perpendicular to the light flux are well illuminated, but all other surfaces are in a deep shadow..

At the same time, it is easy to see that the LED flashlight in the dark is seen from afar much better than other sources. LEDs really have a greater “range”, but for full illumination of an open area, you need several lamps with a carefully organized scheme of their placement and mutual direction.

The intermediate result is this: in small spaces, it makes no sense to organize a complex electrical network and install multiple supports to accommodate LED floodlights. A mercury lamp with a power of up to 100 W is capable of efficiently illuminating an area with a radius of 20-24 meters. If we are talking about really large areas, several LED lights, the lines of light of which intersect many times, will illuminate even the farthest corners.

The principle of operation of LED, DNaT and DRL

But the question of choosing a source is not always limited to the sensitivity of the lighting it produces. To have complete information about the differences between lighting devices, you need to understand the mechanism of their action and be able to correctly classify lamps of different types.

DRL, ESL, CFL are different names for the same type of gas-discharge lamps, the glow of which is achieved by ionizing mercury vapor. The source includes a bulb, the inner surface of which is covered with white phosphor, and an electronic ballast – an electric current converter for igniting and maintaining the combustion of an ionized arc. The key difference between different types of such lamps is the layout and location of the control unit. In economy lamps, it is compactly placed inside the case, DRLs require the installation of additional equipment in the immediate vicinity.

DRL lamp with ballast

DNaT, DNaS – various names for high pressure sodium lamps (NLVD). A burner with sodium vapor, placed in a flask filled with a mixture of inert gases, acts as a luminous body in them. Like mercury lamps, these lamps also require control gear, different from that used for DRL. Nevertheless, the possibility of replacing mercury lamps with sodium lamps exists, and although the latter benefit in terms of luminosity to electrical power, their service life is somewhat lower. The lamps are characterized by a rich and pleasant orange light.

HPS lamp with control gear

LED sources, called LED or SDIS, emit light due to transient processes in a solid – a semiconductor. They are very sensitive to the operating environment, do not tolerate overheating and extremely negatively perceive deviations of the supply current parameters from the recommended ones. The main benefits of using LED sources are their extremely low power consumption and long lifespan..

LED street lamps

The issue of size and ease of placement

As you can see, all of the types of lamps under consideration require the installation of additional electrical equipment. But for energy-saving and LED lamps, auxiliary devices are placed compactly and hidden, and sodium and mercury lamps require the installation of a choke and a trigger device in the technical compartment of the street lamp housing. The connection diagram is simple, but you have to assemble it manually.

In addition, there is a criterion for the completeness of lighting equipment. To install DRL and sodium lamps, a lamp housing and a reinforced bracket are needed, while LED floodlights can be easily mounted on almost any surface or structure.

The ease of use of LED lights is largely due to their low energy consumption. Less costs are required for the device of the power supply network, and in some cases LED lighting can even be autonomous: the daily need for electricity is provided by only two or three photocells.

Light parameters of different sources

To finally understand the difference in the efficiency of a particular type of lighting, the nature of the light emission should be taken into account. Color temperature, predominance of certain parts of the spectrum, luminous flux and color rendition affect not only the convenience of perception, but also safety.

The light temperature of DRL depends on the composition of the phosphor coating and can range from 3500 K (warm white) to 6000 K (sterile white and white-blue). Sodium lamps have a very narrow color temperature range, ranging from 2500–2600 K. LED technology is characterized by the same glow temperatures as mercury lamps. In everyday life, the most popular are white LEDs of the cold part of the spectrum (4000 K and higher), warm shades are much less common.

Color rendering index is a direct indicator of the “assimilation” of light by the human eye. Color rendition is also determined by the degree of distortion of the real color of an object under artificial lighting, the value of this coefficient can range from 10 (very bad) to 100 (very good). For fluorescent lamps, the color rendering falls from 9 to 6 in proportion to the increase in the glow temperature. For LEDs, this relationship is inverse – the warmer the light, the lower its practical utility. NLVD has a color rendering index of 3-4, despite the high illumination density, all objects acquire a yellow-orange tint.

It is worth briefly touching upon the spectral characteristics. For example: conventional incandescent lamps emit in all ranges, from infrared to near ultraviolet. Mixing, waves of different frequencies turn into a stream of soft white light. Mercury and sodium lamps generate radiation in different parts of the spectrum, but yellow-orange, green and blue predominate. In addition, in some ranges of the spectrum, there are “dips”: the lamp does not generate light waves of this length at all, which explains the poor sensitivity of economy lamps to the eye.

White LEDs have no dips in the spectrum, but in the green part of their luminescence (about 550 nm) there is a noticeable decline. And it is in this range that the peak of the sensitivity of human vision perception lies. In addition, there are LEDs that generate light of only a certain frequency with minimal deviations, for example, red (660 nm) or yellow (580 nm).

Maintainability, safety, disposal

When you decide on the effectiveness of your street lighting, be sure to consider a number of practical aspects. For all their shortcomings, mercury and sodium lamps are fairly cheap light sources, besides, they provide for the possibility of replacing ballasts..

When choosing LED lights, pay attention to the quality of the technical implementation of the heat sink. Most of the cheap LED technology is sinning precisely because of poor heat dissipation, which is why there is a rapid degradation and failure of the source..

Choosing DRL and energy-saving lamps for lighting, you run the risk of facing the problem of their disposal. Due to the mercury content, burned-out lamps must not be disposed of with household waste, but must be taken to demercurization centers..

Finally, weather conditions play an important role in the illumination of open areas. Outdoor LED lighting in fog conditions works more efficiently than others. It is also worth remembering that mercury lamps of almost all types in cold weather require time to warm up, and housekeepers shine dimmer and take time to warm up due to the temperature error of capacitors that are part of electronic ballasts.