The development of LED technology has accelerated signifi cantly in recent years. At the present time, the fi rst applications making use of light-emitting diodes in general lighting are emerging. What are the advantages and isadvantages of this technology? And will this technology meet the expectations invested in it?

LED technology is based on the semiconductor lightemitting diode. While the first LEDs only emanated monochromatic light, the development continued rapidly. Momentous milestones were the invention of the blue and, subsequently, white diode, and, later on, the high-power LED. Each year, diodes with a little higher specific power have been introduced. Today, we can encounter in general lighting diodes having approximately 100 130 lm/W, thus theoretically surpassing incandescent and fl uorescent lamps, as well as some discharge lamps. In addition to their high effi ciency, the main advantage of LED technology is considered the long service life. Nevertheless, in practice this parameter depends on many circumstances. Responsible manufactures mostly do not state a number higher than 50,000 hours, more frequently fewer (e.g. 25,000 hours). Other advantages include their rapid start, the possibility of dimming, small size, the possibility of coloured light, resistance to vibrations and frequent switching, and other properties. Moreover, unlike discharge and fl uorescent lamps, LEDs do not contain toxic mercury. However, the LED is still new, suff ers from several hortcomings and has not been sufficiently tried and tested in practice. Significant problems include temperature dependence (the necessity of high-quality cooling), the necessity of a high-quality phosphor for white light, the gradual decrease in luminous flux over the service life and the high price.

LED lamps
2009 marked the fi rst signifi cant development of so-called LED lamps or LED bulbs, i.e. LED light sources with E14 or E27 threads suitable for replacement of ordinary bulbs. Th e highest current inputs are 8W, which in the warm white light variant corresponds to a 40W incandescent lamp. LED lamps are usually off ered in the E14 variant with a candleshaped bulb or the E27 variant in the shape of an ordinary bulb. The service life of LED lamps is usually 25,000 hours, fewer with some variants. The remaining disadvantage is their high price. The LED lamps segment is still new and it is necessary to avoid unreliable manufacturers stating a very long service life without any technical details or proclaiming replacement of bulbs by very low inputs.

LEDs in public lighting
The development of LEDs has also resulted in their gradual application in public lighting. With their parameters, the current LEDs are able to compete with some discharge lamps with lower inputs (approx. 70 100W). Compared to discharge lamps, LEDs have several indisputable advantages: white light with a good colour rendering, usually a longer service life (the LED’s luminous fl ux decreases gradually), easier regulation and more effi cient use of luminous fl ux in luminaries. The disadvantage of LED luminaries is their higher price and the insufficient experience with LED luminaries in practice (a fact abused by some vendors). Yet the fi rst applications of LED luminaries already exist. The bestknown in the Czech Republic is the LED lighting pilot project in Prague’s Smíchov district.

Other uses of LED technology
LED technology off ers many possibilities of use. Owing to easy implementation of various coloured options, LEDs are applied in architecture and design; they even appear in offi ce lighting and are frequently made use of in the automotive industry. In the future, we will undoubtedly encounter more LED applications, yet this new technology will not be replacing tried-and-tested fl uorescent and discharge lamps any time soon.

Michal Staša
Email: michal.stasa@svn.cz
Tel.: +420 224 252 115

The article is from News at SEVEn number 2/2010, which is available to download here.

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