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Energy in buildings


Exposure to daylight has many positive attributes, from aiding visual performance to production of vitamin D and the mood-enhancing neurotransmitter serotonin. Daylight also has much broader and more complex longer-term impacts on well-being, such as enabling proper eye development and the ultraviolet part of daylight is important for hygiene. These are only a small selection of the complex outcomes of the harnessing and alteration of daylight by people, buildings and the wider environment to give interlinked, and often unconscious, physiological, psychological and cultural outcomes.

Bringing daylight into buildings to provide sufficient illumination for many activities for most of the day, even with overcast skies, has been a critical part of building design. Strategies include elongating buildings at higher latitudes along an east–west axis, allowing daylight to enter high into rooms, admitting daylight from multiple sides of rooms, mitigating direct sunlight from producing glare and using light-coloured interior surfaces.

Deeper daylighting of rooms combined with controls that switch-off artificial lighting reduces electricity use, as does locating highly-visual tasks near to daylit building perimeters. However, since the advent of electric lighting, air-conditioning, lifts and escalators, buildings have not only to become larger and taller but also often have deeper plans with limited, or no, daylight penetration.

In many artificially-lit spaces the temporal cues provided by changes in daylight are often absent.This can have serious adverse consequences for occupant health. Daylight is a powerful cue for the maintenance of the human circadian pacemaker that follows the cycle of night and day. It is crucial to the healthy regulation of hormonal rhythms that impact cognitive performance. Properly maintaining daylight-driven circadian rhythms requires a complex combination of light intensity, duration and timing of exposure to daylight, the amount of blue wavelengths in the received spectrum and that daylight’s spatial distribution.

Blue light in the wavelength range 460-480mm is generally more effective compared to monochromatic light of wavelength 555 nm in maintaining a human circadian clock.. Particularly when overcast skies prevail, for spaces away from windows within deeper-plan buildings, the penetration of daylight may not provide healthy spectral luminance requirements..

Luminescent devices using quantum dots and/or dyes with appropriate spectral-shifting behaviour have the potential to

  1. concentrate diffuse solar energy (from cloudy skies) via an externally-protruding light shelve so that a higher intensity is available to provide effective illumination deeper into a room
  2. propagate that initial light deep into a room to reduce the energy used for artificial lighting, and
  3. modify its spectrum to make that light better support human health. Natural variations in initial incident solar illuminance directly produce modulated variations in the output luminant spectrum.

This research supported by the Velux Stiftung, Switzerland, is the first into luminescent devices for daylighting conceived as light shelves that can provide spectral modification. New luminescent materials in novel configurations will be developed for this application. Theresearch encompassesanalytic and theoretical studies utilizingnumerical modelling platforms for the design of luminescent devices for different contexts.For experimental verification, several luminescent devices will be fabricated and characterized.Measured performance of developed proof-of-concept systems will be examined via exposure to a range of real ambient daylight conditions.Techniques for integration of luminescent daylighting devices into buildings using variable transmittance materials will be investigated.

Daylighting and electricity in buildings and the built environment