The variations in the brightness of the bulbs caused by voltage fluctuations of the electricity supply itself are known as flickers and can on occasions be a nuisance for users and cause them discomfort. "The main reason why these fluctuations may occur is industrial machinery that consumes a lot of electrical power at certain moments," explained Izaskun Azcárate, a researcher in the UPV/EHU's Signal and Communications Group. The International Electrotechnical Commission (IEC) established legal limits on mains fluctuation, taking as a reference the response of an incandescent bulb to it. "The industry itself that installs machinery of this type has to ensure that the quality of the mains power supply is not compromised and that the limits are complied with," said the researcher.

With the entry onto the market of new lighting technologies, like compact fluorescent lamps (CFL) and LEDs, it was necessary to determine once again their sensitivity when subjected to voltage fluctuations. The first pieces of research, published in 2008, "indicated that the new lamps were less sensitive than the incandescent ones and therefore no changes in their brightness occurred when there was the same fluctuation in mains voltage," said Azkarate. "What is more," she added, "there were cases in which high levels of fluctuation in the mains were measured and yet there were no complaints by the users."

On the basis of these results, various international standardisation organisations have begun to propose changes in this aspect. Two changes have been proposed: to adjust the flickermeters to the new reference lamps or else increase the established limit. But both changes entail problems: firstly, "today there is not just one type of reference lamp," and secondly, if the limit is increased, other kinds of equipment connected to the mains could be affected by these fluctuations.

Analysing complex signals

"To be able to analyse the validity of these proposals, an exhaustive study is needed of the response of the new lighting technologies to voltage fluctuations," said Azkarate. And the fact is, once the analysis had been completed, they saw that not in all the cases were the new technologies less sensitive.

Measurements were taken using a set of lamps subjected to different types of voltage fluctuations. Firstly, they used standardized fluctuations (analytic signal), and in a second piece of work they used actual fluctuations, which tend to be more complex, registered in four locations in the north of Spain. They concluded that there are three different behaviours: there are lamps that are less sensitive than the incandescent lamps; there are ones that reach the levels of the incandescent ones or even surpass them; and there are others that respond differently depending on the actual signal applied.

"These results cast doubt on the reduced sensitiveness to voltage fluctuations of the new technologies, and reveal that sensitiveness does not depend only on the lighting technology but also on the complexity of the voltage fluctuation and the actual scenario in which the lamp is used," concluded the researcher. "That way," she added, "both the proposal to raise the flicker limits and the one involving the seeking of a new reference lamp appear unworkable."

"The solution could be geared towards controlling the response of the lamps during the design process. To do that, it would be necessary for no lamp to display any sensitivity greater than that of the incandescent bulb," she stressed. In other words, as the research concluded, by maintaining the current flicker threshold, a test protocol should be established whereby each manufacturer could check that in these conditions the lamp does not exceed the threshold.

Additional information

Izaskun Azcárate (Bilbao, 1984), a telecommunications engineer, belongs to the Signal and Communications Group (GSC) of the Department of Communications Engineering of the Faculty of Engineering in Bilbao. There are another five researchers in this research group. Izaskun Azcárate has done this research with a pre-PhD grant from the Government of the Basque Autonomous Community (region). To develop the project, the group collaborated with the IEC (International Electrotechnical Commission), CIGRE (Conseil International des Grands Réseaux Electriques) and with various manufacturers in the lighting industry (Osram and Philips).

Bibliographical References

I. Azcarate, J. J. Gutierrez, A. Lazkano. P. Saiz, K. Redondo, L. A. Leturiondo. "Experimental study of the response of efficient lighting technologies to complex voltage fluctuations". International Journal of Electrical Power & Energy Systems 63: 499-506 (2014). DOI: 10.1016/j.ijepes.2014.06.039I.

Azcarate, J.J. Gutierrez, P. Saiz, A. Lazkano, L.A. Leturiondo, K. Redondo. "Flicker characteristics of efficient lighting assessed by the IEC flickermeter". Electric Power Systems Research, Elsevier 107: 21-27 (2014). DOI: 10.1016/j.epsr.2013.09.005