Buildings are responsible for about 36 percent of Europe's greenhouse gas emissions, and according to the International Energy Agency, lighting accounts for 17.5 percent of global electricity use. Internationally, the trend toward efficiency is highly correlated to economic and infrastructure conditions. Europe and Asia are conservation-minded and open to government programs to limit consumption.
Stricter energy efficiency requirements that have been sought for the past several years are cited as absolutely necessary for the bloc to meet its goal of cutting emissions 20 percent from 1990 levels by 2020. Complimentary to these efforts, European countries are required to establish a certification system to measure buildings' energy efficiency. These certificates will be required for any new construction or buildings that are sold or rented to new tenants. Existing buildings will also have to, during any major renovation, improve their efficiency if at all feasible.
With these mandates, is there a way to make the light “intelligent” such that, in essence, it becomes similar to the human eye and adjusts according to the many light sources – and people – in a room? There is; and the unique approach is to focus on the light not on the power supply. The coming wave of Cognitive Lighting will demand independent smart sensors that are 'environmentally aware' in order to provide not simply data on the surrounding environment, but answers to how best to respond, both to save energy and enhance lighting quality.
Intelligent lighting and daylight
Sustainability mandates and financial incentives have driven many companies to set aside the capital budgets needed to upgrade to more efficient lighting systems. Quite often, the light sources in use, such as T8 fluorescents, are both highly efficient and long-lived, which suggests to many facility operators the need to wait until more efficient light sources, such as LED lighting, mature to the point they show a clear operating advantage before making upgrades. In fact, there are ample incentives to move now, by taking advantage of “daylight harvesting”. Ambient light sensors combining photopic, human-like sensitivity with wide dynamic range are enabling a new generation of lighting controls that may be built directly into replacement lamps and luminaires to shift more of the interior lighting burden onto the available daylight.
Image 1: Daylight Harvesting saves energy while maintaining target interior lighting level to avoid keeping lights on at full power
In a facility with skylights, windows or sidelights there is available daylight, which varies according to time of day, weather conditions and more. Areas that get light from those sources don't necessarily need much artificial light – at least not during the day – but areas farther from those sources do. In a smaller facility, companies often simply turn out the lights on sunny days. The challenge typically arises in a larger sites with thousands of square meters of space where managing each fixture's light output to compensate for the changing amounts of ambient light during the day is an enormous challenge and is impossible to do manually.
To date, facility managers trying to take advantage of daylight have looked to external daylight harvesting sensors that attach to groups of lights. These after-market offerings can provide incremental energy reductions, but still leave substantial savings on the table and have a number of performance issues that result in over- or under-lit areas and jarring jumps or drops in light levels.
Image 2: Photopic response, mimicking the spectral response of human vision, senses a narrower range of wavelengths than a silicon photodiode.