Selecting lighting for low-energy buildings:
The lighting industry is changing very quickly with
several new products being added to the market every
day. The following information is subject to change
as these technologies are updated.
It is desirable to have light fixtures that
complement the daylighting system and provide
maximum energy savings. One must determine the
sensitivity for the lighting in the space. For
general areas, hallways, etc. non-dimming fixtures
are adequate. Areas were detail is important should
use dimming fixtures to maintain constant lighting
levels.
In general, it is desirable to specify the highest
luminous efficacy light available. High-intensity
discharge (HID) lamps, sulfur lamps, and fluorescent
lamps provide good light output with a high luminous
efficacy. Sulfur lamps can be used in large areas
with high ceilings.
HID lamps are also ideal for high areas, but are
difficult to use with daylit buildings. Drawbacks to
this technology are the long re-strike time, and the
ability to dim the lights to low levels. Typically,
the minimum dimming capability is 40% of the maximum
power draw. These fixtures work well in common areas
where cloud cover will not trigger the lights to
cycle "on" and "off" or where
marginal daylighting (bad design!) will never cause
the lights to drop before 40% of capacity. These
fixtures should not be used in conjunction with
motion sensors because of the long strike time.
Fluorescent fixtures currently work best with
daylight applications. The lamp temperature should
be above 5200K so that light matches the natural
light. The short "strike" time allows them
to interact well with motion sensors. T-8 lamps
should be used with electronic ballasts for the best
efficiency. T-5 lamps are just starting to enter the
market and provide additional efficiency over the
T-8 technology. T-12 and magnetic ballasts should
not be used. Compact florescent fixtures may be used
if the lighting design calls for spot lighting or
hallway lighting. These fixtures have a lower
efficiency than longer tubes and should not be used
for large areas.
Three lamp fluorescent troffers can provide much
flexibility in the design of the building. These
fixtures typically contain two ballasts for
providing either one-lamp or two-lamp switching.
Energizing both circuits energizes three lamps. This
provides three levels of dimming capability for
daylighting. In addition, if the one-lamp ballast is
replaced with a dimming ballast, the ability to
modulate the fixture is infinite provided that
proper controls are used.
Zoning Controllers:
Light zones should be defined such that they are
parallel to the fenestration providing the
daylighting.
In many applications, "up-lighting"
provides a good solution for lighting. Since the
bulb is not visible, the occupant does not see
whether the fixture is on or not. This tends to
provide a higher use satisfaction.
Although not directly a part of energy efficiency,
the following information should be specified. The
color rendering index and the total harmonic
distortion should be identified.
Checklist:
- Lights are zoned parallel to windows
- T-8 or T-5 lamps are used
- Total watt density of the lights is less than the 10CFR435 standard. (Target goal is 80% of the standard with good lighting design.)
- No 24-hour security lighting is used. Motion and daylighting sensors control security lighting. This includes egress lighting (or a separate egress system is used.)
- No incandescent lights (including halogen) are used.
- Exit sign lights are low-wattage (less than 4 watts) LED or equal