The likely magnitude of lighting energy savings due to the
replacement of energy-efficient lamps together with control gears
can be estimated via worked examples. Taking a typical daily operating
period of 10 h and 5.5 days per week, the amount of daily,
monthly and annual energy savings from the replacement of the
energy-efficient lighting system were determined and are summarized
in Table 1. The calculated annual energy saving was about
3000 kW h indicating a substantial saving. An energy-efficient light
fitting of high luminous efficacy often means that less amount of
power is required to provide the same illuminance for a given interior
space. As the measured results indicated, the mean illuminance
level is more than the recommended value with less
energy consumption when such energy-efficient lighting systems
are used but retaining the basic luminary layout. It indicates that
replacement of energy-efficient lamp fittings may cause glare
and excessive brightness problems (i.e., the illuminance after energy-
efficient lightings replacement may far more than the required
value). Students may have great difficulty with seeing in
areas of high glare which causes visual discomfort and deteriorates
school environments. However, with the unchanged luminary layout,
relocations of other building services, for examples, sprinkler
heads and air diffusers are not required to save such excess installation
costs. Moreover, visual improvement and further lighting
energy reduction can be attained with proper photoelectric dimming
controls to dim down the illuminance to the required value
[24]. Given that FL,min = 0.05 and FP,min = 0.2 (indicated in a catalogue)
and based on Fig. 1, the further fractional lighting energy
saving of 12% representing 770 kW h/year was computed. It should
be pointed out that the extra capital cost of the dimming equipment
should also be considered for financial justification. The present
study does not include energy saving in air-conditioning which
is due to the heat dissipation from the operation of the lamp fittings
and the control gears. In Hong Kong, the room temperature
is often set at 25 C. When a fluorescent lamp operates inside a luminary,
its ambient temperature rises. Typical values can be 10 C
above room temperature for open type luminaries [7]. Sensible
heat from the electric lights includes convective heat from the
lamps, and radiation absorbed by surroundings and then released
as convective heat by ambient air after a time lag. With less lighting
energy consumption, the cooling load and the overall electricity
use could be further reduced.