Page 56 - European Energy Innovation - Autumn 2015 publication
P. 56
Autumn 2015 European Energy Innovation


Adaptive indoor LED lighting
and user comfort

Spatial light distribution of daylit situations as a reference for user preference

By Martine Knoop, Technische Universität Berlin, June 2015

Light Emitting Diodes Most existing quality measures the preferred conditions and set
have shown a rapid for indoor lighting are derived the minimum requirements for
evolution in the last few from research with and referring an acceptable balance between
years and are replacing to the use of diffuse light sources. diffuseness and directionality for
conventional light sources in The International Commission on room appearance, modelling
luminaires for general, functional, Illumination (CIE 2013) looked and shadows. Research at the
lighting in indoor applications. into the applicability of existing Technische Universität Berlin
In combination with appropriate lighting quality measures in the looks into user acceptance,
controls, these directed light assessment of the quality of measurement and specification
sources can offer task lighting interior lighting with LED lighting of the spatial light distribution
where and when needed. The systems. This review states that of both daylit and artificially lit
resulting adaptive, demand preferred luminance levels for situations. For this purpose, a
responsive, LED lighting solutions the vertical surfaces within the mock-up room at the Technical
can realize highly efficient field of view can be found in University of Berlin is used, that
task illumination. However, in literature (e.g. Loe et al. 1994, Van allows for separation of a large
comparison to illumination Ooyen et al. 1987, Newsham et number of variables that could
with conventional light sources, al. 2004, Newsham et al. 2005, affect the subjective evaluation of
the proportion of diffused and Kirsch 2015). However, further spatial light distribution (Figure 1).
directional light in room changes research is required for the The mock up has self-illuminating
and the resulting lighting diffuseness – directionality of room surfaces of which areas
conditions are not always rated the lighting within the room, the of approximately 20 x 20 cm²
positively by the users. Too spatial light distribution, which can be dimmed up and down
directional lighting could lead affects shadows and appearance (Kirsch and Völker 2013). In Fall
to harsh shadows and interfere of people and objects. 2015, the room will be equipped
with task performance, lead with an artificial sky as shown in
to unpleasant appearances Using daylight as a reference, Figure 1. Spatial light distribution
of people in the room or be being the chosen light source is described and evaluated
distracting or confusing for some from a user’s point of view (e.g. by means of light incidence
users. Additionally to that, the Heerwagen and Heerwagen solids (Liedtke et al. 2013).
illumination of vertical room 1986, Boyce et al. 2003), the Through quantifying spatial light
surfaces can decrease, which preferred directionality and distribution and analysis of user
subsequently may affect room diffuseness could be derived from responses, guidelines for lighting
appearance. daylighting conditions. Schofield design and product development
and colleagues indicate that most will be drawn up.
In order to provide comfortable people prefer diffuse lighting with
lighting conditions the light a directional component, which In summary, adaptive, demand
distribution in a room should be can be found “on a cloudy day, in responsive, lighting has a
considered. This lighting quality the illumination field of a typical great energy savings potential.
aspect seems to be of specific room with an overhead light and Nonetheless, user comfort needs
importance in situations with light-coloured walls, or from the to be considered in designing
smart, adaptive, LED lighting sun embedded in a diffusing sky” these solutions. Lighting of
solutions, as they might realize an (Schofield et al. 2011, p. 2330). room surfaces is required for an
inhomogeneous light distribution appropriate room appearance.
in the room. Research is needed to look into Additionally to that, localized,
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