It’s all to do with the rapid evolution of solid state lighting (SSL), a type of lighting technology made from multiple light-emitting diodes (LEDs). It is known as solid-state lighting because LEDs consist of layers of solid semiconductor materials.
Until recently, LEDs were only available in red or green and were used mainly as indicator lights in electronic devices such as remote controls. However, the emergence of blue LEDs in the 1990s, for which its inventors were awarded the 2014 Nobel Prize in Physics, meant that white light was able to be produced from LEDs for the first time.
Because LEDs convert electricity directly into light particles, SSL is more efficient than other light sources such as sodium street lamps, which produce light as a by-product of converting electricity into heat.
It also emits a wide spectrum of colours and requires no warm-up time, which means it can produce ‘the right light at the right place at the right time,’ according to Peter Bracke, a partner on the EU-funded SSL-erate project.
Health benefits
SSL systems can change the colour, intensity and even the distribution of their light sources in response to the environment by using networked sensors to detect any changes.
This can link to potential health benefits. Some combinations of light level and spectrum can improve alertness in people. Similarly, exposing the eyes to more blue light in the morning cuts melatonin production, reducing fatigue during the day and improving sleep by boosting the circadian rhythm, though only if blue light exposure is reduced at night.
However, as high exposure to blue light may be harmful for the human retina, a good lighting system is carefully designed in order to balance these two aspects.
‘The light sources are easier to tune (for example, dimming, colour changes) and there is more freedom to tailor the optics and the light spectrum,’ said Bracke.
SSL-erate aims to accelerate the uptake of SSL by promoting knowledge-sharing and innovation in the area. The project has launched a website, lightingforpeople.eu, in order to maximise the potential of SSL in cities as well as indoor environments such as offices, schools and homes.
Increased use of SSL could lead to ‘human-centric’ lighting systems, which positively affect our physical and psychological well-being, but Bracke says it must be used wisely. ‘The new technology is no guarantee by itself for good lighting systems and a lack of vision, focus or correct information can lead to inappropriate results,’ said Bracke.
While LED lights can produce the same amount of light using much less energy than current sodium gas lamps, energy savings can also be increased by being smarter about when the lights are turned on. The EU-funded LITES project aims to do this using networks of motion detectors embedded in SSL systems.
“'When there are no people in the street … the lights go to a minimum value.’
‘Our sensors can detect the presence of people in the street, or cars or bicyclists,’ explained Professor Georges Zissis, a partner on the project. ‘When there are no people in the street … the lights go to a minimum value.’ This minimum value varies between 10 % and 20 % of the maximum, depending on the location requirements.
Energy savings
The latest data collected from the project’s pilot sites in Bordeaux, France, Riga Technical University campus, Latvia and the Universidade de Aveiro, Portugal, suggests that intelligent SSL systems can make energy savings of 65 % to 73 %. In addition, they provide brighter and whiter light than current yellow sodium lamps, improving visibility and colour contrast for pedestrians and other users.
However, if street lighting is being turned off when no one is around, could this lead to increased crime rates or accidents in these areas? ‘I have read many papers and I’ve worked in lighting for maybe 30 years now and I have no formal proof that more or less light increases or decreases crime or traffic problems,’ said Prof. Zissis.
Intelligent SSL systems are also being applied to high-visibility public buildings and spaces, such as museums and zoos. The ILLUMINATE project is showcasing what SSL can do in these situations, in order to promote the uptake of more modern and efficient lighting systems.
One of the project’s pilot sites - Belfast City Hall in Northern Ireland – has taken the opportunity to not only save energy, but also design a better, more flexible lighting system. They can tailor the lighting colours and configurations for special events, such as Belfast Pride, the Queen’s birthday, India week & Orangefest, while still saving 67 % on their energy.
A visitor questionnaire given out at most pilot sites before and after the new systems were fitted showed the new SSL systems performed better across most of the parameters measured, such as brightness, visibility and visitor comfort.
Though the SSL systems use less energy, this does not represent the whole cost of a lighting system, as the LED lights and their controllers are currently more expensive to buy and install than traditional sodium lamps and city councils can often pay a much lower rate for electricity usage. However, with operating lifetimes of 10 to 15 years for an LED light, compared with three to five years for a sodium lamp, many new installations can recoup their costs in two to three years.
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