The Independent Power Supply vs. Dependent Power Supply:
The following advantages of Energy Independence in linear tube LEDs are centered on an external
power supply vs. an internal or end connected system. The power supply is often referred to as the
‘Driver’ and this is literally about Driving Change with the LED ‘Driver’. The independent power supply is typically installed in the area allocated for the former fluorescent tubes ‘ballast’ and it connects to the
tube via a wire and clip system. One power supply typically goes with each new LED tube.
Separation of Heat from the Light Emitting Diodes:
Better Color Consistency - Heat is the enemy of the Light Emitting Diode (LED) and Power Supplies
generate significant heat. So, the more effectively the lighting system can separate the heat from the
LED the better. A high performance LED system will protect the phosphor on the diodes. The layers of
phosphor on an LED dictate the color temperature, and the phosphor is vulnerable to heat. Think of the
layers of phosphor as cheese on a slice of toast in a toaster oven. As the oven heats up, the cheese
melts and changes color and eventually burns off. Simply, heat will burn off the layers of phosphor
applied to the diodes and change the color. Power Supplies generate heat, and if they are ‘Dependent’
in that they are internal to the LED tube the heat from the Power Supply will adversely impact the
LEDs. The visible proof of the impact comes in seeing Dependent Power Supply tubes that have run
for 10,000 or more hours, non-stop with chips that appear more blue white that neutral or warm white
as they started. The blue white light is the ‘native’ state vs. the more creamy color as the phosphor
layers dictate. The phosphor has literally been burned off of the chips changing the color in the four to
six inch area where the internal or dependent power supply was located.
Longer Lasting Diodes - A high performance LED system will also protect the diodes from
overheating. As diodes overheat they lose their longevity to perform at the specified output levels. The
visible proof of the impact comes in seeing Dependent Power Supply tubes that have run for 10,000 or
more hours, non-stop and have burn marks on the backside in the exact area where the power supply
is located. As well, the proof comes in running a foot candle meter along the face of the tube and
seeing the drop off in output in the area where the power supply is located. The output is so dramatic
that the foot candles right at the surface of the tube in controlled tests run over 300 fc but drop to 150 fc
at the edge of the ‘burn zone’ and drop to 110 at the center of the degraded area. Since the ‘burn zone’
is typically at least the length of the internal Dependent Power Supply, the degraded area is at least 4 to
5 inches or approximately 10% of an overall 48” tube. Given that these losses occur inside of a single
year of non-stop operation, the lifetime is compromised to several years since the lighting standard for
‘life’ losing up to 30% of the specified output. The typical 1 to 3 year warranty range is logical given the
short-comings of a Dependent Power supply and the damage that is can make on the diodes. Most of
the Dependent Power Supply tubes last about 50,000 hours vs. 80,000 for the Independent Power
Supply tubes. With 8,760 hours in a year, the life span ranges from 5.7 years up to 9.1 years at nonstop
operations. That difference can equate to massive savings in energy consumption.
Component Approach to Servicing the Lighting System
Longer Warranty - The engineering ‘Component’ design approach behind the Independent Power
Supply accepts that the capacitors and electronics in the Power Supply generate heat. Since heat is
not only the enemy of the Diodes, but it is also the enemy of the core semi-conductor chip inside the
diode…the component lets the operator locate the Power Supply away from direct contact with the
LEDs. So, the key is to take the Power Supply as far away from the chips as reasonably possible.
Given that fluorescent tube fixtures are designed with spaces for the ballasts, the ballast location is the
most logical place to position the Independent Power Supply. The cover plates already have the
fastener systems and the ballast already needs to be disconnected and discarded in the retrofit
regardless of the new type of Power Supply technology. The labor is almost equivalent to bypassing
the ballast vs. replacing it.
A high performance LED system will provide up to 5 years because the thermal management will be
sufficient to maintain the color quality and longevity. Given the complexity of the electronics in a Power
Supply it is the ‘Achilles Heel’ of any LED system, and it is most likely to fail before the LEDS lose their
required efficacy. So, when an LED tube with a Dependent Power Supply System fails inside of a
Warranty the provider and/or Manufacturer would have to send the whole tube to the recycling bin and
waste what is often more than 240 semi-conductors in the process. This is far from a logical or
sustainable model, and it is also a tenuous financial risk on the supply side. Many LED manufacturers
are gambling that the Dependent Power supplies will hold up just long enough to make it through the
warranty. Given that an Independent Power Supply costs about 10% of the cost of the tube (Sample:
$7 for the Power Supply vs. $70 for a 4’ 15W LED Tube) replacing a Power Supply is significantly more
cost-effective for the supplier. This perspective on cost speaks to the financial solvency and reliability of
a Manufacturer to meet the obligations of the Warranty. Any company can write a 5 year warranty, but
they need to be able to financially back it up, and the Independent Power Supply provides the flexibility
to do so.
Better Post Warranty Protection - A property owner or manager needs to consider the worst case
scenario. Imagine this situation. The day after the 5 year warranty expires on two tubes, both fail. One
has a Dependent Power Supply and the other has an Independent Power Supply. The owner must
replace the entire tube for the dependent system at the going rate of a new tube. The cost may be ten
times that of replacing an independent power supply. This component approach is proven in other
industries. If the starter fails on a car, the starter is replaced before the car is sent to the scrap yard.
Unfortunately, in a world of increasing disposability, the logic of some manufacturing processes is often lost in the race for market share. Fortunately, buyers have choices, and in many cases the more
prudent choices are comparable in price with dramatically more advantages.
Power Supply Size and Wattage Flexibility
Higher Efficacy via Higher Power Factor - The size of the Power Supply is a key factor in the
efficiency of the whole lighting system. Capacitor size and quality is often restricted inside of very tight
spaces like the channel behind the diodes. Certain manufacturers have identified the problems with the heat proximity to the diodes and the restricted space, but they have only taken a half step to solve it by shifting the Power Supply from the back of the LED Printed Circuit Board (PCB) to the end of the tube.
In these situations, the heat is still adjacent to the PCB so the heat is transferred to the chips and
degrades the phosphor on those chips at the end of the tube.
Perhaps the worst aspect of these Dependent ‘End-Location’ Power Supplies is that they create dark
spots on the output. In an effort to reduce the dark spot on the tube, the engineers are forced to
compress the capacitors and components of a linear Power Supply that is typically four inches or
longer into a double stack ‘cylinder’ power supply that is only typically two inches long. This
compressed Power Supply is typically about 1 1/8” inches in diameter (sized slightly larger than a T8
tubes) and about two inches long. The whole volume is 3.52 cubic inches (3.14 (Π) X .56” (Radius) X 2”
(Length)). By comparison an external
Independent Power Supply does not have the size restrictions to fit inside the tube either along the
back or in a cylinder at the end. This flexibility gives the engineers more room to incorporate larger
capacitors, and the technology can run more efficiently with some ‘breathing room’. As an example the
Independent Power Supplies typically have a volume that is at least twice the size of the equivalent
Dependent Power Supplies at 7 cubic inches or greater.
The Internal Power Factor helps deliver performance. Many internal Dependent Power Supply tubes
produce between 80 and 90 Lumens / watt. This ‘efficacy’ is primarily based on the quality of the
Diodes, however a contributing factor is the Power Factor of the Power Supply. Given the additional
size and room for larger Capacitors, the Power Factor can jump from .86 on internal Dependent Power
Supplies all of the way up to .996 for the external Independent Power Supplies. This simply means that
less electricity is wasted from the source to the chips. So, the less waste increases the ability to
produce the most output at the least cost. A .996 Power Factor only loses .004 of the source power.
More Output Options - An Independent Power Supply gives the property owner or manager options
to select different wattage LED tubes for different applications. As the wattage increases, the size of the
Power Supply increases. So, Dependent systems are limited if they need to pack the electronics inside
of the back of the diodes or the cylindrical end housing. An Independent system provides much more
flexibility given that the location area that was formerly for the ballast provides enough room to expand.
15W - Independent Power Supply for a 15 Watt 4’ Tube 1.5” Wide by 1.12” Deep by 4.5” Long Equals
= 7.56 Cubic Inches This is more than double the volume of the Dependent End-Location Power
Supplies 18W - Independent Power Supply for an 18 Watt 4’ Tube 1.5” Wide by 1.12” Deep by 5” Long
Equals = 8.4 Cubic Inches
This is more than double the volume of the Dependent End-Location Power Supplies.
25W- Independent Power Supply for a 25 Watt 4’ Tube 1.5” Wide by 1.25” Deep by 5.25” Long Equals
= 9.84 Cubic Inches.
This is more than two and half times the volume of the Dependent End-Location Power Supplies.
Installation Ease and Autonomy
Quick Clip Connect System - Installing an Independent Power Supply for an LED tube is as simple
as replacing the ballast in a fluorescent fixture. Given that the panels are designed to conceal the
ballasts, the power supply fits inside the channel. The installation time is approximately the same as
installing a tube with an internal Dependent Power Supply, because the installer still has to open up the fixture and bypass the ballast to the feed the circuit to the tombstones. Many facility managers, have
asked to install an Independent Power Supply for each tube so that in the event of failure, the other
tubes will stay lit. This is a practical convenience in terms of timing to reduce the urgency of replacing
tubes in a whole fixture that may otherwise go dark if the circuit is broken or arching occurs in the
tombstones for a Dependent Power Supply system.
When it comes to the ‘Quick Clip Connect System’, the Independent Power Supply tubes offer
additional ease of installation and maintenance. The clip systems not only protect the circuit continuity,
but they also give the installer the ability to quickly link the tube to the power supply. Likewise, if facility
managers elect to change the tube color temperatures then they can quickly unclip the tubes and clip
an alternate product into position. If any of the Diodes fail in a tube, then the facility managers can also
quickly clip a replacement into position.
Reduced Tombstone Dependence - When it comes to ‘Reduced Tombstone Dependence’ the
Independent Power Supply leads the entire industry. The tombstone is only used to support the LED
tube vs. power it from the end. Facility managers are well aware of the ‘arching’ issues with faulty
tombstones and those same issues that have plagued the fluorescent tubes are also a liability with the
Dependent Power Supply system. This creates a significant maintenance advantage for the
Independent Power Supply LEDs because if there is failure due to the tombstones with the dependent
system then the facility manager needs to climb the ladder to check and repair and the fixture is outside
of the warranty of the dependent tube.
Asymmetrical Features
More Directionality Options - The Asymmetrical Advantage of an Independent Power Supply comes
in several forms. Since each tube is run off of a different supply, the facility managers can chose to
customize the output of one tube over another within the same fixture. The variables include color
temperature, wattage, and the angle of light. Since the tombstone is free of the electrical charge, the
facility manager can angle the LED tube to the desired position.
The Independent Power Supply is the key to flexibility. With a Dependent Power Supply, the only option
is a straight down position given that the tube goes dark when it is rotated in the tombstone away from
the horizontal circuit connection. This directionality feature is particularly relevant in work areas where
certain intensity of light is needed over ambient light. As an example, in a four tube fixture the two
center tubes could be set straight down while the outside ones could be angled at 30% to wash more
light across a room. Or, on a two tube fixture one tube could be angled straight down while another
could be angled at 45% to wash a wall with light. The variables are numerous and the facility managers
can tailor the lighting to their needs accordingly.
Increased Energy Control Systems - The Independent Power Supply provide great flexibility. Given
the increasing demand for Occupancy Sensors, Daylight Harvesting, and Timer controls, the
independent system gives facility manager the high-tech ‘enabled’ options for smart controls. As an
example, a facility may call for reduced foot candles in certain areas at certain times of day. Since each
tube in a multi-tube fixture is powered by separate sources with the independent instead of a bank of
tombstones, the independent system is well equipped for the layers of potential future control needs.
Additional Engineering Advantages beyond the Independent Power Supply:
Deep Fin Thermal Management vs. Shallow or No Fins:
Look for Advanced Thermal Management. A deep fin extruded aluminum heat sink ensures maximum
heat removal away from the diodes.
The SMD vs. DIP:
Choose a tube with Long Lasting LED Chips. Surface Mounted Diodes (SMDs) last longer than their
Dual In-Line (DIP) Predecessors.
Modular Aluminum PCBs vs. Fiberglass PCBs:
Keep your options open with Modular Design flexibility. 12” modular Printed Circuit Boards allow for a
wide range of sizes to be cost-effectively manufactured, and they give you the advantage of replacing
just one of four components if there is failure in the tube. If one tire blows on your car…you don’t have
to change the other three. Since Aluminum is such an excellent conductor of heat, look for LED tubes
that have an Aluminum PCB over fiberglass to help remove as much heat as possible from the Diodes.
The combination of an Independent Power Supply, Deep Fin Thermal Management, and Aluminum
PCB work extremely well together to protect the diodes and increase color consistency and overall
longevity.
Made in the USA vs. Overseas:
Pick an LED tube that is manufactured in America and meets the ‘Buy America’ Qualifications for the
American Recovery and Reinvestment Act (ARRA). You can do this to help support the Green
Economy and job creation here at home and…you can do this to ensure that your product has great
quality control and oversight, faster delivery times, and more responsive warranty support. Overall, the
domestic manufacturing is also comparable to overseas production costs because of certain
automations with tighter tolerances than hand assembly and reduced shipping costs given the weight
of components like the aluminum deep fin heat sink.
CONCLUSION:
Select a Linear ‘Tube’ LED that has as many of the following features as possible:
• Independent Power Supply
• Deep Fin Thermal Management
• Surface Mounted Diodes (SMDs)
• Modular Aluminum PCBs
