The effect of light on health, wellbeing and productivity is the focus of human centric lighting systems. Here, Helvar's Henri Juslen explains their benefits.
14 July 2014
Following extensive studies, human-centric lighting installations are emerging as a way to meet people's emotional needs purely through the control of LED's illuminance levels, colour temperature and direction of light.
In the early 1990s scientists began to study the efficacy of light therapy in the treatment of seasonal affective disorder.
In light therapy, light levels are raised significantly, particularly in the morning, to help alleviate the disruption of the circadian rhythm caused by the reduced amount of natural light.
The circadian rhythm is a 24-hour, endogenously generated cycle that determines sleeping and eating patterns. For the circadian rhythm to work, it is important to have intense, cold light in the morning and darkness (as complete as possible) at night. This cycle can be modulated by external cues such as sunlight, from which human centric lighting takes its cue.
Continued studies in the early 2000s found that in addition to rod and cone cells, the eye also contains other light-sensitive receptors and these are linked with mental alertness. Studies showed that the spectral sensitivity of these receptors was different to that of cone cells - the sensitivity curve of cone cells peaks at yellowish light at 555 nanometers (nm), whereas the peak sensitivity of the previously undiscovered receptors seemed to be in the bluer, colder light at about 470nm.
In practice, this means that our alertness responds to not only to the intensity of light, but also to the colour temperature; from this, we now know that exposure to light can increase alertness much quicker too. This makes sense when you consider natural light itself varies in terms of both intensity and colour temperature, not only over the day, but also as the seasons change.
As this knowledge became more commonplace, luminaire manufacturers soon introduced new luminaires with adjustable colour temperatures. At first, these were luminaires comprising multiple fluorescent tubes of different colour temperatures, mixed at a desired ratio.
This required two controllable drivers for each luminaire. With LEDs, the first versions were implemented using the same principle. However, the DALI Colour Control standard further simplifies the colour temperature tuning of white light. A two-channel LED driver, which has a single DALI address, executes a command sent by the DALI control system and sets the level of lighting and the colour temperature to the level required.
As a result, it is now incredibly easy to employ human centric lighting methodology when it comes to lighting the workplace. In this sense, it is important to consider how varying colour temperatures can affect productivity. As we know, cold, blue light keeps eye receptors alert by maintaining a level of blue light at certain times of the day when productivity may dip - such as after lunch.
This can also be attuned to the seasons too; during winter when light levels are reduced a warmer, more yellow light can be used to help improve the comfort and wellbeing of staff.
Alongside this, overall levels of illuminance also need to be considered. A DALI control system can be programmed to increase or decrease lighting levels according to exterior lighting. As such, a typical system may see illuminance levels set higher or lower at certain times of the day - during the morning and towards the end of the day, lighting levels may need to be increased, according to ambient levels.
Creating an intelligent colour control system is the best way to ensure that lighting levels are in line with changing needs. There are numerous configurations of controls that can be created - an astronomical clock, for example, is one way in which a fully automated system can operate. By installing daylight sensors, which can be linked to the luminaires to adjust levels, lighting can be turned up or down depending on the levels of daylight.
Where manual adjustments need to be made, this too is possible simply by selecting various levels on the colour control system's colour wheel. Ensure that lighting levels are not altered too much outside of the body's natural rhythm, as this can in itself have a damaging effect on emotional wellbeing. With this in mind, it's important to work under the guidance of a lighting specialist that can provide a controllable system that is in line with working hours and changing needs.
Henri Juslen, product development director at Helvar