SIEMENS
Fixture Selection/Energy Savings Analysis
Fixture Selection
Siemens is familiar with both the quantitative and the
qualitative benefits of converting from an HID street
lighting system to an LED street lighting system. The
improvements to the quality of light are founded on the
fact that the system operates in a Mesopic
environment’, and that each lamp type (HPS, MH, MV,
and LED) provides light that is perceived differently by
the human eye. Under the conditions present in a
roadway lighting system, the LED solution can have an
initial lumen output from the fixture that is less than that
of its HID counterpart, and still produce the same
perceived environment depending on the
Scotopic/Photopic (S/P) ratio, which is a correction factor determined by the spectrum of the light
source, as recognized by the industry.
The Siemens’ fixture selection approach is based on the perceived lumen methods, created by the
Lawrence Berkley National Laboratory in July 1995*. This approach has allowed Siemens to maximize
energy savings for customers without sacrificing the quality of the lit environment. While energy
savings is a driving factor for a system conversion, Siemens believes that a properly lit environment is as
equally important as the energy & cost savings LED brings to the customer.
Siemens prefers to use new fixtures over retrofit kits when converting from HID to LED. However, in
some instances using an Original Equipment Manufacturer (OEM) retrofit kit that has been designed for
the existing fixture does make sense. Typically this is done only in the decorative styles, which usually
account for 5% or less of the entire project scope.
All fixtures selected by Siemens are DLC listed, which is the base requirement set forth by Eversource in
order for the customer to get rebates for installing more efficient fixtures. Past projects in New
Hampshire have shown that Siemens is able to install fixtures that get the customer the maximum
amount of energy efficiency rebates.
Siemens’ design philosophy is to assist our customers in determining the appropriate balance between
lighting levels and energy savings. This is a collaborative process which utilizes relevant design
guidelines such as the Illuminating Engineering Society of North America (IESNA) RP-8 guidelines. RP-8
recommends wattages based on route classification and level of pedestrian conflict. Some roads may
transition from commercial to residential and the lighting levels adjust accordingly. Additionally, the
community’s goals and site-specific variations would be taken into account, such as school areas,
crosswalks, or public safety/crime issues. Siemens will provide various options and the financial
considerations associated with each to aid in the decision making process. The end product should be
relatively uniform lighting levels based on street classification and pedestrian activity.
* Luminance Levels ranging from 0.005 cd/m? —5 cd/m*
2 Reengineering of Lighting Photometry, $.M. Berman, LBNL-42327-L-213
9225 Bee Cave Rd www. siemens.usa.com
Building B, Ste 101 $12-837-8000
Austin, TX 78733 Page 17
