● Research Trends and Results

Balancing Energy Conservation by Office Task andAmbient Lighting with Amenability
MIKI Yasuhiro (Dr.Eng.), Senior Research Officer
Residential Environment Planning Division, Housing Department(Keywords) Power-saving measures, energy conservation, task and ambient lighting

2. Example of further renovation to task andambient lighting
We introduced task and ambient lighting withpriority on energy conservation using LED lightsources in an actual office, and then further
renovated it to improve the perceived brightness (Fig.
1). To obtain a sense of spatial brightness with theminimum possible increase in consumed power, weused ambient lighting to illuminate dark areas ofwalls and ceilings. We also surveyed the power
consumption and evaluation by office workers
before and after the renovation. From the results ofthe survey, it was shown that a vast improvement inevaluation by office workers (such as a sense ofspatial brightness) could be achieved afterrenovation even when the power consumption of thetask and ambient lighting method was kept low
compared to the general lighting method (Fig. 2).

Before改修前
renovation改修後
After renovation

Figure 1. Task and ambient lighting before and afterrenovation
2

Power consumption
density (W/m )消費電力密度（W/㎡）

1. Introduction
After the Great East Japan Earthquake Disaster,
many offices conserved power by switching offsome of their lighting fixtures (“reduced lighting”).
But although reduced lighting brings significant
energy-saving effects, it also forms undesirable
lighting environments with dark areas beneathswitched-off fixtures. This problem arises because
Japanese offices most commonly use a generalsystem of lighting in which fixtures are equallydistributed across the ceiling to provide lighting atdesk level.
By contrast, the system of task and ambient
lighting widely adopted in Europe and America isthought effective from the viewpoint of achieving
sufficient brightness at desk level while conserving
energy. This system follows the rationale of “theright lighting in the right place at the right time”,
achieved by using individual desk lamps (tasklighting) to provide brightness at desk level whileslightly reducing the surrounding brightness(ambient lighting). When a position is unoccupied,the desk lamp can be switched off. If properlyplanned, this system can be used to form visualenvironments with a good balance between light anddark while at the same time conserving energy. On
the other hand, merely introducing a different systemof lighting tends not to improve the amenability of
the lighting environment.
In this paper, as a simple example, we introduce acase in which renovations were made to improve theamenability of task and ambient lighting introducedwith priority on energy-saving characteristics, but
without increasing the consumption of energy,
resulting in improved evaluation by users.

20
高評価
High evaluation
17W/㎡

Desktop

Sense of overall office
執務室全体の明るさ感
brightness

1513W/㎡

Brightness over

机上面の明るさ
desk

10(Evaluation（評価値は推定）(Evaluation（評価値は推定）estimated)

estimated)

Neither
どちらでもない

7W/㎡
5W/㎡

5

Task
lighting
タスク照明

Ambientlighting
アンビエント照明
Low
低評価
evaluation

0General or全般もしくはambient lighting
アンビエント照度

lighting
机上面照度

Satisfaction with office

執務室全体の照明の満足度
lighting in general

Hf蛍光灯全般照明
Ht fluorescent1generallighting（推定）

LED全般照明LED generallighting(estimated)（推定）2750 lx750 lx(estimated)

LEDタスク・アンビエント
LED task and3 ambient（改修前）(beforerenovation)

LEDタスク・アンビエント
LEDtask and ambient(after（改修後）renovation)

300 lx

350 lx

750 lx

750 lx4

Figure 2. Relationship between lighting method,energy saving and evaluation
3. Conclusion
While the task and ambient lighting method could
be seen as effective for conserving energy in offices,
the case in this paper shows that the quality of thelight environment needs to be fully considered inorder to balance this with amenability. This researchused the results of the MLIT “FY2010 Basic survey
on methods of evaluating energy consumption forbuilding standard development promotion projects
and commercial buildings” (representative:Tadahiko Ibamoto, Tokyo Denki University).