Sparks Electrical News September 2018

LIGHTING

26

WATERTIGHT LED LUMINAIRES

LED FLOODLIGHT SOLUTION FOR UNIVERSITY OF STELLENBOSCH RUGBY FIELD

S mart [3] by Gewiss is a new watertight LED luminaire range available in three versions: Smart [3]; Smart [3] S and Smart [3] C. This Gewiss patent is designed, devel- oped and produced in Italy. The fitting is distinguished by an el- egant design highlighting the particular features of the new LED technology: reduced energy consumption, high impact resist- ance and quick, easy installation. The product was developed to become the first LED lighting solution with exceptionally high protection of IP69. The opal or transparent shield with longitudinal faceting makes the fitting A lthough LED lamps, fittings and drivers are available in dimmable and non-dimmable options, any light emit- ting diode component is dimmable. An LED is a current controlled electronic component, very similar to a rectifier diode or a transistor. With these types of devices the voltage drop across the component, which can vary slightly between batches of a particular model number, is a function of the applied current. For this reason, if the LED lamp does not have a control circuit inside, a constant current LED driver must be used. A ‘voltage mode’ LED such as, for instance, a 12 V ac lamp or a 24 V dc strip LED will always have a built-in voltage to current converter. The graph in Figure 1 shows the typical light intensity versus the current flowing through an LED rated at 350 mA nominal current. It is thus possible to adjust the light intensity by simply varying the dc current through the LED component; this is called analogue control. The control method is very popular amongst typical GU10 type dimmable LEDs where the internal driver converts the RMS voltage from the dimmer into a corresponding constant dc current, thereby achieving a linear dimming. There are a number of technological advantages to analogue dc current control, such as, it is a mature technology ideally suited to 230 V ac to dc current converters, especially where physical space is limited (such as in GU10 LEDs); there are many circuit design choices and control ICs available; it is cost effective, especially for 230 V ac to dc current control applications; and it has a quick response time to varying power supply conditions. Furthermore, an application advantage of dc current control for LEDs is that there is no high frequency flicker if the current is a pure and constant dc, thus the flicker percentage and flicker index are both zero. Unfortunately, analogue current control does have disadvantages: it is costly to achieve very accurate control owing to component tolerances; possible LED colour shift can occur; and it is difficult to achieve very deep dimming, especially when the LED characteristics can vary. Because of these disadvantages, this control method is usually reserved for integrated types of LED lamps where the internal driver is matched to a specific LED component. There are many applications where a dimmable LED module must be controlled by an external driver. To avoid the disadvantages of analogue control, most external LED drivers and some professional integrated drivers employ digital dimming control. In most cases, Pulse Width Modulation (PWM) is the chosen for the simplicity and maturity of its technology. PWM control differs fundamentally from analogue control: it does not vary the dc level of the current. The output current of the driver is a fixed dc matched to the LEDs nominal rating, but the current is turned off and on, as seen in Figure 2. By reducing the ‘on’ time, the average current to the LED reduces, and it dims. This digital dimming method provides numerous advantages: it is accurate if the dc current is accurate; there is typically no LED colour shift as the LED experiences only its nominal current; true and accurate 0% to 100% is possible; reliable and repeatable behaviour between

ideal, not only in industrial contexts but wherever maximum attention to visual comfort is important. The body is made of polycarbonate, so the device may be installed in food-related environments too. Ideal for areas with a high degree of humidity or a high concentration of dust, Smart [3] may even be installed in car parks and garages, outdoor areas, under-roof shelters, in warehouses, circulation and storage areas, supermarkets, railway stations, bus terminals and shopping centres.

Enquiries: ACDC Dynamics, +27 (0)10 202 3300

FUNDAMENTALS OF DIMMING LEDS

FIGURE 1: Relative intensity versus dc current of a typical 350 mA LED.

THE DANIE CRAVEN RUGBY C-FIELD at the University of Stellen- bosch is used for training purposes, and this project is the first LED installation on a campus of this size. The field is illuminated by BEKA Schréder’s OMNIstar-maxi LED floodlights, installed on 35 m high masts, in preference to a high intensity discharge (HID) 1 kW metal- halide floodlight. The field has an average horizontal illuminance of 350 lux. The OMNIstar was the preferred LED luminaire. This LED floodlight offers a real alternative to luminaires equipped with high-power traditional light sources, with the added advantages of an LED solution: low energy consumption, improved visibility with a colour temperature close to daylight, limited maintenance, longer life, and instant switch on/off, enhancing the athletic environment and minimising light pollution for the surrounding population. The OMNIstar has been designed to provide an unrivalled combination of performance and flexibility for lighting areas where high lumen packages are needed while offering maximum savings in energy and maintenance costs with a short payback time. This modular luminaire can be installed on a high mast with a bracket of one, two or three luminaires to provide the lighting distribution and lumen package needed to meet the specifications of the area to be lit. BEKA Schréder locally develops and manufactures LED lighting products, designed and suitable for local conditions. The company is proud to be associated with the University of Stellenbosch and Element Consulting Engineers in providing a successful LED solution for this project.

FIGURE 2: Digital PWM dimming.

FIGURE 3: Dimming a ‘non-dimmable" LED strip.

manufacturing batches is achieved; and the technology integrates well with other digital technologies. There are, however, some disadvantages: it is more costly to implement for typical ‘GU10’ type lamps; and there is a possible strobe effect so it should not be employed in industrial applications where rotating machinery is used. A main advantage of PWM digital dimming is that certain traditionally ‘non-dimmable’ LED lamps can be dimmed. For example, a typical 12 V dc or 24 V dc LED strip has an integrated voltage to current converter which allows it to be powered from a non-dimmable dc power supply. By simply wiring a bell-press or rotary digital dimmer or ‘dc dimmer’ between the power supply and LED, as seen in Figure 3, the strip can be perfectly dimmed to a very low intensity, without any damage to the LED or the power supply.

By MC Smit, Shuttle Lighting.

Enquiries: +27 (0)21 510 8900

Enquiries: +27 (0)21 448 8229

SPARKS ELECTRICAL NEWS

SEPTEMBER 2018