30 JULY/AUGUST 2017 LEDsmagazine.com
indoor lighting | LED TUBES
may be to install LED fixtures with a control
system that has been fully tested with the
selected fixtures, and is guaranteed to deliver
high-performance dimming, energy savings, and a comfortable light environment.
Tools such as the Lutron High Performance
Fixture List ( lutron.com/findafixture) can
help inform the selection process.
If you decide to use a TLED retrofit, it is
important to consider efficiency, optical quality, product lifetime, and dimming needs.
Each scenario presents different tradeoffs for
the overall efficiency of the system. In Scenario
1, the ballast must convert the line voltage to a
regulated current and voltage. The electronics
in the lamp then must re-regulate the current
and voltage specifically for the LEDs.
This double-regulation creates additional
losses in the system as compared with Scenarios 2 and 3. In some situations, TLEDs
will have to simulate the filaments in the
ends of a fluorescent lamp, which often
causes additional losses and decreases in
efficiency. Scenarios 2 and 3, which use dedicated LED drivers, will typically provide
higher system efficiency.
In a new construction or major renovation
project, the design team takes great care to
ensure the selected luminaires provide adequate lighting for the space. The photometrics of various fixture types and manufacturers are analyzed and compared to determine
the best solution for the space.
In all three TLED scenarios, the difference
in optical characteristics between LEDs and
fluorescents is an area of common concern.
Most LED tubes do not have a light distribution pattern that matches fluorescent lamps.
Specifically, most TLEDs do not emit light in
an even 360° pattern as fluorescents do, and
some TLEDs have a beam pattern as low as
105°. This may cause fixtures using these
lamps to disperse light differently, or to alter
the amount of light available in the space or
on desired horizontal and vertical surfaces.
The existing fixture reflector is specifi-
cally designed to use light from all outgoing
angles of a fluorescent lamp to throw an even
illuminance below the fixture. Replacing the
fluorescent lamp with a TLED, which is not
omnidirectional, can cause the illuminance
distribution to become uneven, which in turn
can create nonuniformity on the work surface.
TLEDs are often designed to provide a
similar number of lumens out of the fixture
but out of a smaller aperture. This typically
results in more concentrated luminance
and possibly creates glare for the occupants
of the space. To determine how a particu-
lar TLED design will affect lighting levels,
a 2014 independent study conducted by the
DOE reviewed various TLED designs in com-
bination with several different styles of fix-
tures. The study concluded that the only way
to accurately predict resulting light levels is
to individually test each TLED with each fix-
ture ( http://bit.ly/2r5TfOP).
Finally, some lesser-quality LED drivers
(whether integral or external) can cause flicker
that didn’t exist when fluorescent lamps were
used. Because LEDs change their light output very rapidly in response to any changes in
input current, any power fluctuations caused
by a driver will result in visible fluctuations in
the light output (flicker). Lesser-quality drivers
can also be prone to “passing-through” normal
power line disturbances, which are present in
many commercial installations, and can manifest as flicker or shimmer.
In many Scenario 1 situations, a TLED is
used with a ballast that has already been
installed for a significant portion of its
expected life. If the ballast is not replaced at
the same time as the TLED is being installed,
the benefit of adding that long-life LED lamp
is reduced from a maintenance standpoint.
If the ballast fails before the lamp’s expected
FIG. 2. In the UL Type B TLED retrofit scenario, an installer would remove the ballast
and connect line voltage directly to the existing sockets, then plug in a TLED with an
integrated line-voltage driver.
FIG. 3. While more labor intensive than the first two retrofit options, wiring in a new
LED driver along with installing TLEDs and removing the fluorescent ballast, the UL
Type C TLED retrofit scenario ensures compatibility of all components of the system.
Choosing a TLED retroft solution is a careful
balance — ease of installation versus cost