Professor Wilkins says it’s ‘plain enough’ that bad flicker from magnetic ballasts in schools can impair learning. A switch to high frequency gear, or LED luminaires, would fix the problem.

Four fifths of British school children are having their learning impaired and are at risk from anxiety, migraines, headaches and even dyslexia from flickering lighting, an expert scientist has warned.

Because of the way magnetic ballasts manipulate the 50 Hz sinusoidal waveform of the input voltage, they deliver a light output that flickers at 100 Hz. This frequency is in the danger zone of harmful flicker, which could impair learning.

Arnold Wilkins, emeritus professor at the University of Essex and a leading expert in photosensitivity and physiology, says distracting flicker in the UK’s schools needs to be addressed.

‘Unfortunately 80 per cent of our schools are still lit with lighting that flickers at 100 hertz’, he told a Lux conference on lighting fixture design in London this month. ‘It causes headaches and its causes anxiety. It’s there all the time. Whether it impairs their learning, seems to me to be plain enough.’

Although people can only directly perceive fluctuations at frequencies up to about 70 Hz, human vision is adversely affected by light fluctuations up to 200 Hz. Visual performance is especially degraded by flicker in the 100 Hz to 200 Hz range and in general, younger people are likely to perceive lower level and higher frequency flicker than older observers.

Professor Arnold Wilkins says that 100 Hz is present all the time under magnetic ballasted fluorescent fittings in schools. ‘Whether it impairs their learning, seems to me to be plain enough’ he told the Lighting Fixture Design Conference in London.

‘There’s a huge range of susceptibility in the population with those [who get] migraines at one extreme. And it probably contributes to dyslexia but we don’t know for certain.

‘100 hertz should be avoided.’ The solution is to upgrade to high frequency control gear for fluorescent or LED. ‘It’s a simple as that.’

Flicker at 100 Hz is prevalent in older fluorescent light fittings with magnetic ballasts which were popularly installed in schools before the introduction of high-frequency electronic control gear and LED panels. Typically, magnetically ballasted fluorescent luminaires will exhibit flicker of between 10 and 20 per cent of output, and a ‘compact flicker degree’, or CFD, of over 20 per cent.  Prolonged exposure leads to eyestrain, headaches and anxiety.

Professor Wilkins has a number of high profile awards to his name, including the Leon Gaster Memorial Award, the Walsh Weston Memorial Award and the Owen Aves Medal and has been made a honorary fellow of the College of Optometry.

LED Ceiling panels are available from Novel Energy Lighting. We stock multiple quality brands, such as Thorn, Ansell, Philips, and MEGE:

flicker free · led 600x600 · LED Ceiling Panels · led flcker · led panels · low flicker · Novel Energy Lighting · school lighting

changing colour temeprature · controllable lighting · human centric lighting · led panels · led tubes · Novel Energy Lighting · school led · school lighting

Tunable-white lighting is one of the biggest trends in commercial lighting. LED developers have taken a serious grip on the photo-biological research being produced by university departments and other groups. We know more about the way that humans function than ever before and you might say that it’s fortunate for the LED community that the science appears to support a practical technology that is perfectly suited to LED exploitation.

Tunable whites use colour mixing

Standard LED colour-mixing uses red, green and blue channels that are adjusted to deliver the entire range of the colour spectrum. Tunable-whites work in the similar way, using of a number of controllable channels to adjust the colour temperature of the luminaire’s white light output. The channels in a tunable-white system all produce white light, but with varying colour temperatures, from a warm tone to a cool tone.

Inevitably, there are levels of sophistication involved in tunable-white systems and it’s vital that the specifier understands not only what is required from the lighting, but also what any particular system is capable of delivering.

Simple systems use two lines of LEDs

Take a warm white LED and sit it next to a cool white LED and cross-dim between the two. Job done? Well, not quite. It’s true that the cheapest tunable whites work in exactly this way. The most basic tunable linear systems use LED strips mounted side-by-side. One channel will be close to 2700K in colour temperature, with the other up around a cool 6000K. The LED strips are mounted inside an aluminium extrusion fitted with an opal diffuser, which does the colour mixing as the light passes through it. It’s very simple engineering but satisfies a basic market with low performance expectations.

Multi-chip versions do the mixing at chip level

More products are using ‘multi-chips’ where a number of tiny LED chips are combined into the same module. This means that the colour mixing occurs as the light leaves the module. Their very small size means that tunable-white products can be made much smaller, so we’re starting to see downlights using the technology as well as linear systems. These multi-chips tend to have a higher performance specification than the individual LED strips, but nothing should be left to chance.

Colour rendering can be compromised

A lot of fuss is made, quite rightly, over the way that white light presents surface colours. We’ve come to expect a good quality of colour rendering, regardless of light source. Tunable whites are not exempt from this issue but it’s not always clear from manufacturers’ data how well a system is performing.

Cheaper products may advertise good colour performance at the extremes of the tunable range, where light is being delivered from either the warm or the cool channel, but there’s no certainty that the mixed light performs equally well. Generally speaking, the greater the number of channels, and systems vary from two-channel to five-channel, the better colours will look under them.

Not all tunable-white systems cover the same colour range

If there is one aspect of tunable-whites that the specifier needs to take great care over, it’s the colour temperature range that’s on offer. While some systems offer a wide natural ‘circadian rhythm’ range that shifts from candlelight to daylight, there are other systems with a much smaller range, from 2500K to 4000K, which should only be considered as a decorative option.

There are three ways to control the tones

• The simplest systems use manual control to alter the white outputs. Expect to see a wall-mounted control panel or a hand-held remote control that enables you to adjust the colour of the light and the amount of light output. There is nothing scientific about this. It’s left entirely to personal preference, which may – or may not – be a good thing.
• Some tunable controls are designed to replicate the effect of dimming on a filament source, where two things happen at the same time. As the light output is dimmed, the lamp warms up in the same way as a traditional tungsten filament lamp. This is still a manual control method, but has the benefit of mimicking a filament light source. The tunable range tends to be very small, again mimicking the conventional tungsten lamp.
• More sophisticated control strategies are designed to manipulate the circadian rhythm of room occupants. This means that the lighting settings are programmed into the control architecture. Shifts in colour temperature and light level can be pre-set or can be instigated by a manual over-ride. This is the method that’s being used in recent school installations in Scandinavia.

Three discrete channels could be a solution

It’s been pointed out that not all ‘tunable-white’ mixing requires a full colour range. Complex tunable-white schemes mean that you should be able to call up any colour temperature within the mixing range. But some clients will call for specific colour temperatures, often those that are commercially available, such as 3000K, 4000K, 6500K. If that’s the case, then it may be simpler – and cheaper – to consider having three discrete lighting channels operating separately within a bespoke housing.

Photo credit: Glamox Luxo

colour temperature · LED downlights · led lighting · led panels · Novel Energy Lighting · school lighting · tunable light · tunable wite light

Education is no longer about teaching; it is about creating a stimulating learning environment. Or to put it another way the quantity of information given out by a teacher is less important than the amount of information taken in by a student. This shift in emphasis has impacted the design of education buildings. Previously they were designed around the needs of the teacher whereas they are increasingly designed around the needs of the student. This requires more flexible spaces suitable for formal teacher led sessions and also for less formal group discussions and breakout sessions.

Building design has also developed as the importance of daylight to learning rates and attendance levels has begun to be understood. Therefore modern learning spaces tend to receive significant levels of daylight which in turn leads to significant energy savings in well-designed lighting installations.

Best practice

The European Standard EN 12464-1:2011 Light and lighting – Lighting of work places Part 1: Indoor work places provides recommended lighting levels for academic buildings. However whilst important these recommendations address only a part of the lighting requirements. Education is a communication centred discipline and lighting of people so they appear friendly and so that body language is readily visible is important, as is facilitating the use of all presentation materials and formats. EN 12464-1:2011 also provides recommendations for cylindrical illuminance to ensure good lighting of verticals, 150lx at 1.2m height. It discusses the modelling index, the ratio between the horizontal and vertical flow of light, to provide the correct balance between light and shade. It also highlights the importance of lighting room surfaces to make a space feel light and airy and prevent a sensation of gloom, recommending an average illuminance of 75lx on the walls and 50lx on the ceiling.

Education should always be centred on the needs of people and care should be taken not to design spaces for technology at the expense of comfort. However in some areas of high DSE use care should be taken to take account of the effect of lighting on screens. Recommendations for lighting for DSE are provided in the European Standard EN 12464-1:2011 Light and lighting – Lighting of work places Part 1: Indoor work places. However these criteria are for general computer technology and if plasma screen technology is used tighter control of luminaire brightness should be considered. Ideally the balance between lighting for people and lighting for technology should be achieved by intelligent use of lighting controls and scene setting to allow lighting to be adjusted to the needs of the moment.

Taking control

Supplying comfortable and effective light is not the same as supplying controlled and energy-efficient light. A lighting system should interact with the space, dimming in response to increasing levels of daylight, turning on or off in response to occupancy within the space, and with increasing use of technology and the need for flexibility of learning styles allow lighting scenes to be set to provide the optimal conditions for the needs of the task at hand. Lighting should be an integral part of the space ambience, giving a calm or lively atmosphere dependant upon the needs of the subject, providing an inspiring and stimulating environment for students and staff.

Visit www.novelenergylighting.com to explore LED lighting retrofit options for your school or university project. Please call us to discuss options or arrange for light designs: tel. 0208-540-8287, email: sales@novelenergylighting.com

LED downlights · led lighting · led panels · led tubes · Novel Energy Lighting · school led · school lighting · university lighting

energy efficient financing · LED lamps · led lighting · led panels · led tubes · Novel Energy Lighting · salix · salix funding · school led · school lighting

LUX Magazine, 12 JUNE 2014

LED · LED lamps · led lighting · led tubes · Novel Energy Lighting · school lighting