A Modular Approach to Lighting
Enabled by 3M™ Light Tubes
3M Optical Systems Division
3M Electronics and Energy Laboratory
John Wheatley, David Britz, Michael Meis, Vadim Savvateev,
Will Edmonds, Gilles Benoit, Ken Epstein, D. Scott Thompson
Bringing Brilliance
to
Light
Contents
Executive summary.............................................................................................1
A New Design for LED Lighting............................................................................2
Demonstration: The 3M™ Light Tube.................................................................3
Singular Advantages............................................................................................4
Quantum Dots: A Primer.....................................................................................5
Learn More.........................................................................................................5
3M’s model light design demonstrates
how modular components can provide
precise light placement, improve
thermal management and achieve
significant reductions in energy
consumption. 3M is also demonstrating
a new way to enhance color.
Executive summary
The technical and economic barriers to wide-spread LED adoption continue to drop. Bright, durable,
low-cost LEDs are widely available, and are forecasted to become even brighter, more durable and less
expensive in the next few years. (The U.S. Department of Energy estimated that the cost of warm-white
LED packages fell from $36 to $18 per thousand lumens from 2009 to 2010 and will drop to approximately
$2 per thousand lumens by 2015. )
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As a result, LEDs are expanding beyond high-value consumer electronic devices (such as televisions,
mobile phones and computer displays) into ubiquitous applications, from industrial and commercial lighting
to outdoor illumination.
Several technical barriers remain, however. These include:
• Thermal management: LEDs emit about two-thirds the heat of comparable compact fluorescent bulbs
and often less than a quarter of the heat of incandescent bulbs. Despite that extraordinary advantage
relative to other technologies, heat emission remains a concern because the heat is concentrated in
the LED footprint. In some applications, the LED is located in an area where heat can negatively impact
the system, for example in food and refrigerated display cases. This heat can increase system costs
because of damage to illuminated products or additional power required to remove the heat.
• Light transport and delivery: As LEDs have improved in output, efficiency, and cost, their advantages
and use relative to competing sources (fluorescent and incandescent) have increased as well. Initial
applications of LEDs in distributed area lighting use arrays of large numbers (hundreds) of LEDs. The
heat is distributed with the source, and achieving directional control and light quality can be also
challenging. Importantly, the improvements in LED output, efficiency, and cost now enable pairing with
new light distribution technologies that enable remote sources, enabling systems with key advantages
over arrays.
2
• Color: LEDs without phosphors generally emit blue light. Phosphors in the LED package are generally
used to provide a more balanced color spectrum, but can have angle-dependent color and generally do
not provide good rendering of longer wavelengths. Color variations among LEDs can also be significant;
this creates added costs for selecting LEDs from specific bins or bin ranges.
3M is demonstrating a modular light design that addresses the first two technical barriers (thermal
management and light transport), and improves key aspects of the third (color uniformity). By addressing
these limitations in current LED systems, the model design allows for increased efficiency and the potential
for significant reductions in energy use in important applications.
This modular light design achieves these results by efficiently transporting light, separating LED
illumination from LED heat, and thereby enabling higher system efficiencies. The design employs 3M’s
light management materials, which efficiently guide, mix, and shape light to deliver the required output
while minimizing optical losses. It also provides an opportunity for a highly efficient solution for improving
color uniformity (reducing or eliminating LED color variation effects and angle-dependent color). 3M is
making this model design available to the lighting industry to enable progressive end users to advance and
differentiate their lighting solutions while simplifying their supply chain.
1 U.S. Department of Energy, “LED Frequently Asked Questions,” May 2011,
http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/led_basics.pdf
2 J. Wheatley, et al. “Efficient LED light distribution cavities using low loss, angle-selective interference
Transflectors,” Optics Express, Vol. 17, Iss. 13, pp. 10612–10622 (Jun. 22, 2009).
http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-17-13-10612
1
A New Design for LED Lighting
3M is among the world’s leading authorities in managing light. The company’s
multilayer, nonmetallic mirror films, light-directing optical films and reflective polarizers
made the first LCD TVs, laptop computers, and mobile phones a practical reality.
3M has now adapted several of
these technologies for use in LED
lighting. Its model light design
consists of an LED light engine
and a polycarbonate tube that has
been partially lined with highly
reflective (> 98 percent) 3M™
Enhanced Specular Reflector
(3M™ ESR) mirror film. A section
of the tube’s length is not lined
with ESR; this creates an aperture
that runs the length of the tube.
The aperture is covered with a
strip of microstructured, lightdirecting film (Fig. 1).
Light is injected at one or
both ends of the tube. The
3M ESR reflects the light
multiple times, transporting
it down the tube and mixing
it to produce a uniform color
and distribution. As the light
propagates down the tube,
a portion exits through the
aperture with each bounce.
As it exits the tube, the light
is concentrated and directed
by the microstructured film,
resulting in an engineered
light distribution pattern –
light where you want it.
LED
LED
Polycarbonate Tube
Figure 1: 3M LED lighting model
architecture, side and end view. Light
from one or two LEDs is injected into a
polycarbonate tube that has been partially
lined with 3M ESR mirror film; the light
escapes through an aperture that runs the
length of the tube. As light escapes the
tube, it is concentrated and directed by a
microstructured film.
3M ESR
Aperture with
light directing optics
LED
Light Directing Optics
1
2
3M ESR
Aperture with
light directing optics
Figure 2. The illumination pattern
can be changed by changing the
microstructured film.
LED
This model can be adapted to achieve various configurations of brightness, illumination
area, and distribution. Changing just one component allows for a wide range of
potential products. It also provides an elegantly simple architecture where different
light output distributions
can be achieved by using
different replicated
structures for the aperture.
2
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Figure 3. Examples of types of
illumination patterns that can be created
by altering the microstructured film.
Intensity
Intensity Cross Section
Figure 4. Angular output of the 3M Light
Tube: Angular distribution for lengthwise
(0°) and orthogonal (90°) axes.
Polar Angle (degrees)
By changing the configuration of components, 3M’s modular design allows for precise
directional control of LED light. The output distribution for one configuration model is
depicted in Figure 4; in this example, the distribution is very narrow along one axis and
broad along the other. By altering the components—particularly the light-directing
microstructured film covering the aperture—other output distributions can be achieved.
Demonstration: The 3M™ Light Tube
The 3M™ Light Tube is a demonstration of the model design enabled by 3M’s component
approach to lighting.
One application of the 3M Light Tube is in refrigeration display case lighting, where its
design provides excellent illumination along with a very significant reduction in energy
consumption. This application is timely given new energy efficiency standards proposed
for commercial and walk-in refrigerators.
To demonstrate this application, an 18 ft (510 L) commercial vertical refrigeration display
case was retrofitted with a 3M Light Tube system. The system incorporated two 56-inch
long, 1-inch diameter 3M Light Tubes, each with a light output of 550 lm and an efficacy
of 80 lm/W. Overall efficiency (3M Light Tube output/light engine output) is 88 percent.
3
Figure 5. The 3M™ Light Tube
demonstrates the model design enabled
by 3M’s component approach to lighting.
Power Input for
Light Source
Compressor Power for
Cooling Light Source
Total System Power
Number of LEDs
Fluorescent (65W)
65 W
20 W
85 W
—
LED Strip
35 W
27 W
62 W
288
3M Light Tube
14 W
10 W
24 W
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Table 1 compares the heat and total system power use for this cooler using three lighting
systems: 65-watt fluorescent bulb, strips of discrete LEDs (288 in total), and an LED
system using two 3M Light Tubes. Each 3M Light Tube was illuminated with two LEDs
(one at each end) for a total of four LEDs.
Table 1. Comparison of three lighting
systems for a refrigeration display case.
3 See: Juliet Eilperin, “Obama Administration Proposes New Energy Efficiency Rules,” Washington
Post, 29 Aug. 2013.
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Optical measurements were made on the brightness and uniformity at a representative
target plane in the cooler. The 3M Light Tube system produced comparable brightness
and improved uniformity compared to the LED strips.
The differences in energy consumption were notable. The 3M Light Tube system requires
just 24 watts (for lighting and cooling)—72 percent less than the power needed for a
comparable fluorescent lighting system and 61 percent less than the power required by
an LED array lighting system with comparable illumination.
The 3M Light Tube system enables this large energy reduction because it requires less
energy for light generation and less energy for refrigeration (since it introduces much
less heat into the cooler). The LED engines of the 3M Light Tubes are capable of being
placed outside the thermal envelope of the refrigerator and are thermally coupled to the
refrigerator door’s metal frame, using the structural members as heat sinks. For this
example 10W of heat was generated, and improvements toward zero watts are possible.
These results are notable in their own right, and serve as an indicator of the potential
inherent in this modular approach to lighting design. By changing components—
particularly the microstructure on the light-directing optical film that covers the
aperture—the distribution of light can be tailored to achieve the optimum efficiency,
thereby reducing power requirements. Additionally the remote source enables innovative
approaches to thermal management.
Singular Advantages
As noted earlier, the 3M Light Tube is designed to provide bright, uniform, highly efficient
illumination. The model light design’s efficiency and scalability make it suitable for
illuminating a variety of spaces, from small coolers to large rooms.
With the lamp providing
Other advantages include:
directional control, new
• Modularity: each of the key components can be modified individually to best suit
the specific lighting requirements of the application. Lighting designers also have the
option to purchase either individual films or assembled lighting units from 3M.
• Design freedom: unique lighting effects and form factors can be achieved by
altering any of the model light design components. From a luminaire standpoint,
these directional control lamps change the traditional paradigm in which the light
source emitted light and the luminaire provided the directional control. With the lamp
providing directional control, new design freedom exists for luminaire innovation in
cost, performance, and style.
• SKU reduction: the model light design’s flexibility allows simple changes in
configurations to achieve different distributions. This, in turn, allows one base
fixture design to provide a variety of outputs by changing only one component.
Quantum Dots: A Primer
4
design freedom exists for
luminaire innovation in cost,
performance, and style.
Quantum Dots: A Primer
The model light design also provides a unique opportunity to change the spectral distribution of
LED light and hence color quality by incorporating remote phosphor or quantum dots into the
lighting system.
Quantum dots are nanoscale spheres of semiconductor materials. A quantum dot will absorb
relatively short wavelengths of light and emit a narrow spectrum of light at longer wavelengths.
Smaller dots produce shorter wavelengths; larger dots produce longer wavelengths. By adjusting
the quantum dot coating formulation, one can produce a wide range of emission spectra with
engineered shapes, peaks, and designed color attributes.
Because the wavelength of the emitted light is determined by the size of the dot, the emission is
predictable and tunable. When the light from a blue LED strikes a 3-nanometer quantum dot, it
emits narrow wavelength green light. When the blue light strikes a 7-nanometer dot, it emits a
narrow wavelength red light. By controlling the size of the dots, the spectral output of the lighting
unit can be tuned precisely.
Alternative methods for changing the color of LEDs—such as phosphor coatings or the
supplementing of conventional blue LEDs with red and green LEDs—are effective but have well
known disadvantages. Quantum dots have been considered a promising option for some time,
and recently with the help of 3M optical design and film manufacturing capability have been
introduced to the consumer electronics display market.
3M™ Quantum Dot Enhancement Film (3M™ QDEF) is an already commercialized method
for deploying quantum dots in remote light conversion architectures in liquid crystal displays.
Currently, the film (composed of red- and green-producing dots in a matrix material) is being
combined with blue LEDs to generate a white light with spectral peaks in the red-green-blue
primaries. This output configuration allows LCDs to produce saturated primaries and, in turn, a
larger color gamut.
When a lighting application calls for a warm, flattering light, the model 3M Light Tube design could
allow for a 3M QDEF film to be inserted across the aperture. Photons escaping the tube would
pass through the aperture to the 3M QDEF and be converted to longer wavelengths. The spectral
output could be precisely tailored to match the designer’s specifications for color temperature
and CRI. (3M QDEF also has light-diffusing qualities that can soften the light output angular
distribution.) Because the aperture in the 3M design is remote from the LED, lifetime of quantum
dots would be increased due to the lower incident light flux and operating temperature.
Learn More
3M Optical Systems Division continues to refine its model architecture and its first demonstration
of that architecture, the 3M Light Tube. The company is eager to share its latest advances and
apply its technologies to the individual lighting needs of global brands and OEMs.
3M also offers its full portfolio of light management films, including reflectors, directional films
and QDEF.
For additional information, contact David Britz, 3M at (651)736-1901, dabritz@mmm.com.
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3M Optical Systems Division
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