There are three main factors that can significantly reduce energy
consumption.
The use of
full cut-off fixtures ensures that all of the energy used
is directed to the task of lighting the ground beneath the fixture.
This means that a lower wattage lamp can be used to achieve the same
level of illumination compared to the wattage of lamp in a non or
partial cut-off fixture. Typical energy savings of 20 to 30%.
The second factor is to
design lighting to meet the minimum level of
illumination needed. Overlighting wastes energy by making the area
brighter than it needs to be for the required task. You see this in
gas stations and parking lots where the illumination levels are
sometimes 5 to 10 times higher that those recommended by IESNA. The
mentality seems to be is that if a little light is good, than a lot
of light must be great. There is also an economic factor at work.
There is some proof that consumers will choose to patronize the
brighter establishment because they have been taught to believe that
bright equals safe. So some stores have decided to have lighting
wars, where the brightest lit wins.
The third factor to be considered is whether lighting is actually
required for a given task. This is where the most energy is wasted.
You can see this in every major shopping center. After closing, empty
parking lots are lit for no reason. There should be a curfew
provision that requires that parking lot lighting be reduced to 25%
or less within 2 hours of closing.
You also see this in roadway lighting. There are no studies that show
any reduction in accidents by lighting entire roads. The only
conclusive studies that show a reduction in accidents are in what are
called "conflict zones". These are intersections and ramps. However
over the last 30 years power companies have been very successful
lobbying state and local governments to light entire roads. They have
sold this practice to the governments as an matter of providing
increased safety, but no scientific studies have ever supported this
claim. Some studies have actually concluded that lighting roads may
contribute to an increase in accidents because drivers feel "safer".
Feeling safer they tend to drive faster than they would normally
drive and can't stop in time to avoid obstacles that are beyond their
limited range of vision at night.