An HF-ballast increases the fluorescent lamp’s working frequency to approximately 40 kHz, and in doing so lights the fluorescent lamp completely evenly without flashing. At the same time efficiency is improved by approximately 10%.
An HF-ballast ignites fluorescent lamps in a controlled manner. The warm start means that uneven emissions from the cathodes are avoided, which is considered to extend the life span by up to 50% where the switching on and off rate is deemed as normal. Using a warm start HF ballast, the cathodes are pre-heated before the fluorescent lamp receives its ignition pulse. In addition, modern high quality HF-ballasts have a function that significantly reduces or completely cuts this pre-heated current once the fluorescent lamp has ignited. An important function when taking energy savings into consideration, but also it means the T5 light source is powered under optimal temperature conditions.
When discharging starts and the fluorescent lamp ignites, the HF-ballast regulates all unnecessary parameters for an even luminous flux independent of fluctuations in the supply voltage. Furthermore, the HF-ballast monitors the function of the light source and switches it off if defects occur. There are HF-ballasts on the market that can indicate, via the light source, that a mains voltage fault has occurred, for example, over voltage.
A great deal of thought must be given to cable routing when designing luminaires for HF-ballasts.
Internal wiring to the fluorescent lamp must be routed in a way that does not impair functionality. Too long internal wiring to the fluorescent lamp can also cause interference issues (EMC).
Furthermore, the incoming mains cable must be taken into consideration. The mains cable, due to EMC requirements, must not be routed together with internal wiring. For this reason luminaires usually feature a separate channel or row of clips to correctly route these cables.
Master-slave solutions, where two interconnected luminaires are fed by a single HF-ballast placed in one of the units, can only be recommended for HF-standard and where internal wiring can be kept shorter than 1 m. Master-slave solutions for HF-dimming are not recommended due to the very high risk of defective functionality (different light levels from the luminaires).
In the master-slave solutions for Dimming, only the control signal from the HF-ballast of the master luminaire should be considered; this then controls the HF-ballast in the slave luminaire, which is not the same procedure as the one described above.
Life span HF-ballasts
The life span of the HF-ballast is, like other electronic equipment, limited. It is determined by, among others, component selection, mains fluctuations, ignition rate and first and foremost the ambient temperature inside the luminaire. The electronic components’ fault frequency causes failures on a few HF-ballast during the first hours of operation. HF-ballast faults then occur evenly over a period of time, like fluorescent lamps.
The life span and function can be jeopardised by incorrect handling during installation. The HF-ballast can be destroyed by:
- Incorrect measuring of the insulation resistance.
- Current peaks caused by machinery at the workplace.
- Over temperature, if the luminaire is used in a space with increased temperature (normal temp. > 25 °C). The luminaires’ ta (max permitted ambient temperature) is in most cases 25 °C, but luminaires with heightened ta are available.
The life span of the HF-ballast, as previously described, is dependent in part on the ambient temperature. Normally there is a temperature control point (tc-point) on the HF-ballast, which should be checked when the ballast is positioned in the product in question. The tc-max varies between manufacturer and type and defines the highest permitted temperature to prevent damage to the ballast. HF-ballasts with a high tc-max are not necessarily better than models with a low tc-max. The HF-ballast manufacturer may have chosen to place the reference point at a cool or warm position on the HF-ballast.
The life span of an HF-ballast is stated at a specific temperature on the tc-point. Sometimes this corresponds with tc-max, but it can also be stated at a lower temperature. Manufacturers usually state 50.000 hours as the life span with a maximum depreciation of 0.2 %/1000 hours, which corresponds to a 10 % dropout.
The cooler the tc-temperature, the longer the life span. A rule of thumb is that a 10° reduction in temperature on the tc-point doubles the life span while a 10° increase in temperature halves this.
HF-ballasts for demanding environments, HF Industry
HF Industry is a ballast designed for use in rugged and demanding environments. Examples are industrial environments where:
- Mains voltage transients are a problem.
- The atmosphere is dustier than normal.
- The atmosphere is slightly more humid than normal.
- Heavy vibrations occur.
The HF-ballasts are designed for a life span of 100.000 hours (10 % depreciation) under the condition that the temperature is kept below specific levels (according to the spec. for the HF-ballast). They are also designed with IVG (Intelligent Voltage Guard) which both warns and protects against overvoltage and undervoltage. The HF-ballasts are also designed to withstand mains voltage transients up to 4 kV. The more robust HF-ballast offers longer maintenance intervals, which reduces maintenance costs to a minimum.
Ballasts are not available in HF-dim or in slimline designs, which means they cannot be used in all luminaires. The ballasts are primarily intended for products in industrial environments, products that are usually equipped with high lamp outputs and where there is physical space for the HF-ballasts. The use of these HF-ballasts in other types of luminaires, for example office luminaires, does not normally give any advantages compared to using HF-std.
For product ranges, please refer to the industrial luminaires chapter.