Darkness without secrets: technologies and norms for lighting systems
Lighting and signal devices are of great importance also for agricultural machinery. From incandescent headlights to the recent LED systems, the technology has been developed to ensure increasingly greater illumination power and a longer life for headlights. Standards for the type-approval of lighting systems are coming in as of January 2016 with the application of the European Union Mother Regulation
Day and night, in rain or shine, in fog and snow, tractors must be able to operate in all weather and environmental light conditions to ensure the maximum level of safety for the driver. To improve visibility for the driver and other vehicles, a series of illumination and visual devices including so-called lighting groups, as defined in the Highway Code, must be installed. Moreover, greater visibility must be guaranteed for performing operations in the field in low light conditions, a practice becoming more and more common for lengthening work time.
The most recent norms for type-approval (see box The new norms) stipulate that lights will have to be type-approved to comply with the international UNECE Regulations applied to automobiles.
From incandencence to LED
The first headlights mounted on automobiles were the incandescent filament type which are still in widespread use, also in agriculture. These components for illumination are economical and produce excellent luminous chromatic efficiency but they have a brief lifespan for this efficiency. Considering visible light as measured in lumens, a unit defined in part by the differing sensitivity of the human eye to different wavelengths of light in relation to power radiated, the typical value is only 10-15 lumens/watt.
Halogen headlights came along more recently and are now the most popular in the automotive field as well as in agriculture for low beam and high beam performance as well as for work lights. Light is produced by a tungsten filament sealed in a quartz glass envelope usually containing a combination of argon and nitrogen. The tungsten filament receives electricity from the car’s battery and heats up to around 3,000 degrees Celsius thus starting to glow through an incandescence process. At this temperature, tungsten particles burn off the surface to combine with the halogen in the inert gas in the bulb to form a halide of tungsten. Switched off, the halide tends to redeposit the tungsten on the filament to substantially lengthen the brightness lifetime which, compared to similar filaments, is even doubled compared to incandescent bulbs. Also luminousity is greater, typically 20-25 lumens/watt.
In the field of agriculture, two new technologies have been gaining ground even more recently, Xenon and LED. Xenon headlights take advantage from the so-called arc lamp because the light is produced by an electric arc formed between two tungsten electrodes in a bulb of quartz glass containing xenon gas under high pressure, plus mercury and metallic salts. The light produced is very bright and intense with a chromatic content similar to that of sunlight. The electric power consumed by these headlights is usually low-voltage, down to a few dozen V, but they require a high voltage pulse for starting of up to 60 kV for the most powerful lights. To avoid allowing the arc to go out immediately after the high voltage surge, a boost current usually two or three times greater than the nominal voltage lasting less than 0.25 s is generally provided. The typical lifespan of these lamps runs to a few thousand hours and they are usually limited by the corrosion of the electrodes. Moreover, the deterioration of these component materials evaporate due to the high temperatures and condense on the inside surface of the quartz envelope to diminish the light produced. The corrosion of the electrodes can be speeded up by an incorrect polarity of the electric tension or excessive oscillation, ripple, of the intensity of the current. The luminousity created is very high, up to 100 lumins/watt and the average lifetime of these lamps is five times that of halogen lamps. Also available are small xenon lamps with continuous spectral power distribution with various color temperatures. Unfortunately, the cost of these components is fairly high at present due to the need to equipment them with automatic height adjustment to align the headlights to suit the load the vehicle is currently carrying and wipers.
Then the evolution of headlights took a great leap forward with the adoption of LED, Light Emitting Diode. The LED system is able to create a wide range of colors, including a color temperature of about 6000K with a spectrum similar to that of sunlight. These lights have an extremely great luminousity potential and low electric consumption with an efficiency of 100-150 lumens/watt. They also require no maintenance and have an extremely long lifetime of 50-100,000 hours. Moreover, with no moving parts they are very resistant to vibrations and shocks. As with other lamps, it is important to cool as much as possible the heat produced which greatly reduces the luminousity potential and lifespan. Typically the size of the illuminated field is usually comparatively small so a luminous dispersion layer is required which means equiping the LED system with a reflector such as Fresnel diffraction lenses or other optical solutions.
The diodes which illuminate
LED is the acronym of Light Emitting Diode, that is, diodes which emit light.
This system dates back to development in the 1960s as a way to exploit the optical properties of semiconductors which emit light when activated by voltage applied to a stream of electrons. In practice, photons are generated by the normal function of a p–n junction diode, that is, an interface between two parts of a semiconductor to which are added other materials, called drugging. In detail, LED uses semiconductors with a yellow base drugged with arsenic, phosphorus and, more recently, nitrogen.
This element is used for clear light LED which uses flourescent compounds for white radiation effectively simulating the luminous spectrum of normal lamps. Varying the quantity and concentration of flourescent powders makes it possible to achiev light tones from cold white, similar to the light of flourescent lighting, to a cold white yellowish close to the light issued by incandescent lamps.
The new norms
January 1, 2016 marks the official application of Regulation (EU) No 167/2013 of the European Parliament and of the Council, more well known as the Mother Regulation which becomes the reference document for EU wide type-approval norms for tractors, trailers and interchangeable towed equipment.
The purpose of this change is to simplify previous norms in the form of numerous fragmented Directives and regulations dating back to Directive 2003/37/EU. These are now bundled in a single norm, or nearly, which brings in many new features for agricultural machinery. Among them is the fully adopting of various other UNECE regulations. These are international standards which apply to the automotive sector, norms on glass, acoustical warning devices, rearview mirrors, seatbelts and tires as well as lighting systems.
From the legislative point of view, the Mother Regulation refers back to the Commission Delegated Regulation (EU) 2015/208, a thick document which provides the technical details of the various issues. Devices designed to illuminate the road (headlamp) or to emit a light signal are taken up in Annex XI and XII, along with the various UNECE regulations referred to in Regulation 208.
Mandatory control
of damage
The new type-approval regulations extend to agricultural what applies to the automotive sector, including the obligation to install devices which control damage of lighting systems, especially for turn signals.
However, the present devices mounted do not recognize LED lighting so they would signal damage. This means that modern LED lights would be required to be equipped with an electronic circuit to act for the illumination self-surveillance by a surge which simulates the presence and efficiency of the bulbs. An example is the 21W bulb used for turn signals. In the case of damage done to a single LED in the light, the surge is not generated and an alarm is activated to signal the defect to the driver.
Inclination regulation of lights
Other than the lighting and visual signal devices required by law, agricultural machinery is always equipped with a series of work lights which can often be adjusted for the height of the beam. The device changes the inclination of the beam projected, usually in a conical configuration, according spread and the intensity for the area illuminated.
This is why a combination of lights regulated to different settings, possibly for different types, can satisfy the specific needs of operations. The case may be that more profound vision may be needed ahead for driving a vehicle on the road whereas to the rear it would be a good idea to concentrade the beam close to the equipment hitched behind.
