An LED driver is a self-contained power supply that has outputs matched to the electrical characteristics of your LED or array of LEDs. There are currently no industry standards, so understanding the electrical characteristics of your LED or array is critical in selecting or designing a driver circuit. Drivers should be current-regulated (deliver a consistent current over a range of load voltages). Drivers may also offer dimming by means of pulse width modulation (PWM) circuits. Drivers may have more than one channel for separate control of different LEDs or arrays.
definition from led center

Mean Well’s Cost Effective PLP-60 PCB Type LED Power Supply. A nice built-in design for low cost applications.

LED Drivers should not be looked at as inefficient devices. Here is an example of a press release for a 96% efficiency device.

LEDs without drivers?!?! YES! Acriche™ 4W AC LED from Seoul Semiconductor can be directly plugged into the AC line voltage without a converter or separate power supply. (Watch your fingers!)

So as you can see an LED driver is the type of device that comes in many flavors. It depends on your system wattage needs, for the associated cost increase. In an attempt to recycle reuse and repurpose we, here at EcoBrooklyn, decided in a ‘build it forward’ , commonly associated with a ‘green builder’, attitude, to find some drivers of our own. With some ingenuity and help from our friends (our thanks to you) I undertook the idea of using computer ATX power supplies as a regulated Voltage source. Since an LED is a current driven device any fluctuation in voltage even down to a tenth of a volt can cause a large increase in current flow. This can damage or destroy the LED at worst or cause flickering at best, which can have quite a discomforting effect. So with this in mind and the knowledge that computer electronics are very sensitive to voltage fluctuations on a small but reasonably similar level, I had a great match up. Other standard functions include short circuit, over load, over voltage protections and over temperature shutoff. As well as more than one voltage source in the original package. This we can use to allow more than one type of LED being powered by such VCCS (Voltage controlled current source) supplies.

Here are some beginner to intermediate level projects. These are fun things you can do with LEDs while you learn about the technology and its uses…Plus its productive! Also remember, you do this at your own risk. (but I don’t know anyone that has started a fire with 5v. Survival situations don’t count.)

This instructable shows how to wire up one or more LEDs in a in a basic and clear way. Never done any work before with LEDs and don’t know how to use them? Read this Instructable!

Do it Yourself Ambient Light.

Hot glue LED diffusions

LED Task Lamp

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LED Lighting is an important design issue that we take into consideration, importantly due to being a green builder leading sustainable construction practices in Brooklyn we have to stay on top of new technology. In short to ‘build it forward’ is not just a catch phrase it is a feeling and belief in resourcefulness and efficiency. Part of this is due to the fact LED lighting is the single most readily available technology, on the green revolution market, that can make an impact to our total power consumption. As a country in whole, this technology can not be ignored. Its benefits are obvious when LED lighting is taken into consideration.
Like all technology, there are advantages and disadvantages. It is up to us to realize the big picture and not always count on our selfish intentions as a reason to be apathetic. There is a ripple effect in our actions. In other words, it might be an increased up front cost that will be useful for up to 20 years! Our inability to see the purpose of buying a $30 LED bulb when a current incandescent light bulb costs $2, may in fact turn out to cost us more in the long run. (Replacement bulbs at 2k hrs compared to 50k 0r 100k LED is already 25-50 replacement bulbs. At $2 a piece? How many trips to the store in your car is that? How many miles in shipping for replacement bulbs is saved? Then we can count the LED runs at about 10% the power of incandescent. So you are saving up to 90% of your lighting power consumption with LED over 10-20yrs depending on total lamp hours. Lighting can be up to 20% of your electricity bill in normal circumstances. How about the electricity to run the store that stocks those bulbs. There are many more things behind the scenes then we take into consideration.

Here is an excerpt from a brochure on LED technology. Full article link here.

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LED: The next generation of lighting technology

LEDs have some significant characteristics making them excellent general lighting sources:
high source efficacy, optical control, extremely long operating lives and exceptional delivered
lumens when used in a properly designed lighting system. In addition, LEDs also have a
number of other favorable attributes. However, there are important technical limitations that
must be understood in order to properly utilize these marvelous light sources in luminaires.

LEDs – A Little History

Light Emitting Diodes (LEDs) have been around since the 1960s. For the first few decades,
the relatively low light output of LEDs and narrow range of colors limited their role to
specialized applications such as indicator lamps. As LED output improved, the devices
found their way into signage of all types (think LED exit signs and traffic signals) and
into smaller, more decorative luminaires. LED light output levels gradually increased
over time. The past few years have seen white LEDs more than triple their light output.
These improvements have set the stage for LEDs to become the light source for the next
generation of general lighting products.

The State of LED Technology Today

LEDs are solid-state semi-conductor devices that produce light. Because of the way they
are constructed, the light they produce is highly directional. As with any light source,
LEDs have certain characteristics and limitations which need to be understood before the
technology can be utilized to its maximum potential.

LEDs that are designated for general lighting use are expected to produce a suitable level
of light output to allow for the replacement of the existing lighting technologies in use today;
incandescent, fluorescent, mercury, metal halide and high pressure sodium. For most general
lighting applications, white light is preferred. An LED can produce white light in one of two ways:

Phosphor conversion in which the LED chip emits blue or near ultraviolet light. The
LED chip is coated with phosphor, which interacts with the emitted light to produce
white light. This is similar to the way in which light is generated by a fluorescent lamp.
Most of the discussions in this brochure pertain to high brightness or power LEDs
using blue light conversion.

RGB (Red, Green, Blue) systems mix the light output from three or four
monochromatic LEDs (amber can also be used to increase the color palette)
producing white light that is “tunable” to many different colors of light, including
white light of various color temperatures.

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A Typical High Brightness LED in its package
The most important measurement for any LED system is the temperature at the point
within the LED package labeled as the junction. The junction temperature is the primary
determinant of the potential operating life and performance for an LED. The LED manufacturer
designs the LED package for optimal heat removal from the junction. Once the luminaire
manufacturer has the packaged LED, the junction temperature is controlled by the design
of the luminaire and the ambient temperature environment in which it operates.

Being a Green Construction company in Brooklyn, NY we like to recycle, reuse and re-purpose materials. Electronics are no exception. This post is about heat sinks. LEDs like to run at about 25 deg C or 70F. Led manufacturers give guidelines for heat sink size and configuration. With this information you can re-purpose a computer processor heat sink. Most PC processors are equipped with a circular heavy duty heat sink. This is usually more than adequate depending on the power of your LED. Another technique for helping cool the LEDs is through an electronic technique called PWM or Pulse Width Modulation. For example, if the LED was to stay on for say 1 sec. (arbitrary) we can electronically switch the led on and off in rapid succession. Persistence of vision will give you the same effect as a moving picture…..a perceived continuation without interruption. This is typically done in a 1000% power for 10% of the time duty cycle. This allows the heat sink to be working on dissipating heat 90% of the time and only absorbing it during the last 10%. With this in mind you can use High power LEDs in tight configurations while not overheating them. Here are some heat sinks I re-purposed for an air cooled lighting demonstration.

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In a press release from Jan 2009 it is stated that the pentagon is installing more than 4,200 recessed LED luminaries in Wedge 5.They are expecting a payback of less than four years with a reduction of 22% in overall electricity usage. A total reduction of 140 tons of CO2 per year. They even found out that the LEDs reduced their cooling costs. The HVAC system does not have to deal with excess heat radiated from traditional illumination methods.

http://www.cree.com/press/press_detail.asp?i=1231279088576

“The U.S. federal government is taking a leadership role in energy efficiency for federal buildings both through existing mandates, as well as President-elect Obama’s American Recovery and Reinvestment Plan, which calls for the renovation of public buildings to make them more energy efficient,” said Chuck Swoboda, Cree chairman and chief executive officer. “Installations of highly efficient, low-maintenance LED lighting, like these in the Pentagon and in the U.S. Federal Reserve, demonstrate that the future of energy-efficient lighting is here today.”

So with the understanding that any experiment should be undertaken with the proper materials. I set out and found a large supply of computers and harvested anything I could use, before they were sent off to be melted down. (Or crushed) After 7 hours of unscrewing, unclipping and moderate finger jabbing I end up with around ten power supplies and a nice assortment of heat sinks.

Including a few large aluminum ones great for cutting into a shape adequate for the calculated LED heat sink needs.

Small current LEDs do not need heat sinking but also put out relatively little light. For general lighting LEDs you have to use high output LEDs typically in the 350 Mah to 1000 Mah current range compared to your blinking led on your cell phone which typically takes about 20 Mah.

This increased amount of electricity pushed through a small device increases the heat radiated by the excited material causing the light. To keep the LED from burning out you simply attach some efficient heat conduction to the reverse side and draw the heat out into the air. Even with heat sinks on the smaller side of the calculated range of acceptance….you are still at a considerably lower temperature than a normal light bulb. You can touch both led and heat sink with your hand without harm.

This is great when safety comes to mind. How many 3V fires have you heard of? Very few compared to the popular 300V floor lamps that have burned so many houses.

From Christopher Annis

LED lighting is not a new idea. It is only in the last few years or so that the technology’s efficiency and efficacy surpassed CFL and HID lighting. This makes it hard to find cost effective lighting replacement, without large upfront cost.  But at Eco Brooklyn we are passionate about improving the energy efficiency of Brooklyn brownstones and constantly tinker with the technology to see how we can use it in our building. So let the experiments begin!

LEDs are typically DC devices that can be powered either through a controlled Voltage or Current drive source. Voltage sources have to be stable. Any tiny fluctuation in voltage can cause a purportionally greater current spike. This translates into flickering lights.  On the other hand, Current driver circuits are expensive and yield low wattage, high efficiency configurations. This can cause an unreasonable cost associated with powering each led fixture.

To explain the difference between the two power source terms I will use a small analogy.  Think of electricity traveling through a wire as water through a pipe.

Voltage = ‘Pressure’ of electricity

Current = ‘Amount’ of electricity

If you happen to have a dead computer around then you might have a working voltage source. Your computer power supply can be converted into a stable voltage source with a high wattage rating. (Added benefits include built in protection against over voltage, short circuit, open circuit, temp, and just about anything else that could cause a safety issue. )

To drive an LED from a Voltage source you need to put a Resistor in series with the LED. This is a good way to create a simple stable voltage controlled current source.  What kind of resistor do I use? Well here is a calculator for figuring out your LED resistor needs. You will just need some of the information from your specific LED’s limitations.

http://led.linear1.org/1led.wiz

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