At last, a production LED that approaches the efficacy of good fluorescents (100 lumens per watt).
I saw this announced at the Lightfair tradeshow this week. I expect to post more on other subjects later. Now admittedly, this doesn't include power loss in the power supply (ballast), but we're getting there. I'll be interested in how the light radiates and how much they cost as well, because that will make or break it in the long term.
Thursday, May 7, 2009
Saturday, May 2, 2009
Biggest Barrier to LED lighting
Okay, there are several barriers, and it could be easily argued that there are more serious ones than this. I believe the biggest problem with LED lights will be shortened life to to overheating in standard fixtures (I believe short CFL life is most often caused by overheating, and I'm not convinced that Energy Star or other standards address this). Most fixtures that have been designed for edison-base incandescent bulbs are not designed to remove the heat from the fixture or bulb. Instead, the fixture is designed to withstand the heat (ever see a label on a light fixture that requires 105 C rated wiring?). Some of the worst offenders, as far as keeping the heat in, are recessed lights that are rated for insulation contact. This means that the fiberglass (or blown-in) insulation can completely cover the light fixture inside the ceiling. We did some testing with Illumra wireless relays in the ceiling box and found that even with a 40 or 60 watt incandescent bulb, the wiring box could reach 80 or 90 degrees C.
Okay, enough background, why is this such a big deal for LED lights? Put simply, like any electronic device, LEDs do not like to be hot. It shortens their life a lot. For the physics behind this (if you care) the Arrhenius equation gives you some idea - doubling the temperature doesn't just cut it's life in half, it cuts it much shorter. You see, most light fixtures have been designed to take light from a (fairly focused) point source, the filament in the bulb, and diffuse it evenly over a space. Putting lots of LEDs at one point concentrates the heat, making it harder to keep the LEDs cool. Spreading out the LEDs is a good solution, but then the fixture isn't designed to take light from many points and distribute it.
I've seen a number of LED lights in a fluorescent tube form factor, but with most (or all?), the LEDs radiate only out one side of the bulb, defeating the reflectors in the fixture, preventing the light from shining where it should. In an office environment, you would probably get very uneven lighting with this solution (until they start mounting the LEDs 360 degrees around the tube).
The real solution is to design the fixture from the start with LEDs in mind. This will require a "ballast" (really a power supply) that provides a constant current to run the LED string, along with either failed LED bypass or failed LED indication (if each LED is removable). I suggest that, if a standard small form plug-in LED module included a small parallel LED with a large value resistor, then when that LED fails (open) the small cheap LED would illuminate to show which module(s) need to be replaced. Otherwise we'll be in the same situation as with a string of holiday string lights, when one bulb is slightly loose, the whole string fails to light. The whole string should be driven with a constant current (for most even illumination). Typical drive currents are 350 mA, and if the correct number are arranged in series, the voltage of the string could be set not far below the voltage provided by a rectified AC line voltage, which will help with efficiency (using a switching constant-current power supply with AC line power factor correction is even better - see my earlier posts about that).
More to the point of overheating, spreading the LEDs around a large surface helps solve the problem. Imagine a standard office ceiling fixture with 4 T8 fluorescent tubes. Remove the tubes, then cover the surface of the internal reflector with LEDs. The heat is spread out, the whole string can be in series, and when one cartridge fails, the small red LED shows you which one to replace. This solves most (if not all) of the issues with LED lights. Old fixtures could even be retrofitted with this solution without requiring complete replacement of the fixture. With a more expensive "ballast," dimming could be supported for daylighting or load shedding. As I've mentioned before, however, phase-cut dimming is not a good idea. Either powerline-based data communication or wireless control (insert shameless plug for Illumra products here-remember I work for them :-) is the only good option for dimming the lights. The extra cost (in the bulb/ballast/fixture) to support phase cut dimming (just so you can use your old "standard" wall box dimmer) is not worth it.
Two unrelated notes:
One, I've been adding new features recently to the firmware in many of the Illumra dimmers and load controllers. From day one, we've always tried to select default operating modes that are the most convenient for the users of the products. At the same time, while they save energy as much as possible, we don't want their operation to be intrusive. For example, if a receiver is set up to turn off the lights when the space has been unoccupied for a while, for a time, after the lights turn off, if occupancy is detected, they turn back on. However, California Title 24 (which includes regulations updated in 2005 for how these devices must operate) doesn't allow automatic turn-on when you enter a room. We're making Title 24 compliance the standard operating mode for our receivers, even though it's potentially more intrusive (meaning you must turn on the lights manually when you first enter the room). It's been a tough decision, but since an automatic-on mode is available, we'll still support modes that require less intervention. Perhaps if you are ever irritated by a light that could turn on automatically, but doesn't, you can remember that you may be saving a little more energy (and money) that way.
Two, while I won't be there personally, if you're in New York next week, drop by our booth at the Lightfair tradeshow. Illumra products will be shown in one part of the EnOcean Alliance booth, as well as integrated into a number of products under various brand names throughout the show.
Okay, enough background, why is this such a big deal for LED lights? Put simply, like any electronic device, LEDs do not like to be hot. It shortens their life a lot. For the physics behind this (if you care) the Arrhenius equation gives you some idea - doubling the temperature doesn't just cut it's life in half, it cuts it much shorter. You see, most light fixtures have been designed to take light from a (fairly focused) point source, the filament in the bulb, and diffuse it evenly over a space. Putting lots of LEDs at one point concentrates the heat, making it harder to keep the LEDs cool. Spreading out the LEDs is a good solution, but then the fixture isn't designed to take light from many points and distribute it.
I've seen a number of LED lights in a fluorescent tube form factor, but with most (or all?), the LEDs radiate only out one side of the bulb, defeating the reflectors in the fixture, preventing the light from shining where it should. In an office environment, you would probably get very uneven lighting with this solution (until they start mounting the LEDs 360 degrees around the tube).
The real solution is to design the fixture from the start with LEDs in mind. This will require a "ballast" (really a power supply) that provides a constant current to run the LED string, along with either failed LED bypass or failed LED indication (if each LED is removable). I suggest that, if a standard small form plug-in LED module included a small parallel LED with a large value resistor, then when that LED fails (open) the small cheap LED would illuminate to show which module(s) need to be replaced. Otherwise we'll be in the same situation as with a string of holiday string lights, when one bulb is slightly loose, the whole string fails to light. The whole string should be driven with a constant current (for most even illumination). Typical drive currents are 350 mA, and if the correct number are arranged in series, the voltage of the string could be set not far below the voltage provided by a rectified AC line voltage, which will help with efficiency (using a switching constant-current power supply with AC line power factor correction is even better - see my earlier posts about that).
More to the point of overheating, spreading the LEDs around a large surface helps solve the problem. Imagine a standard office ceiling fixture with 4 T8 fluorescent tubes. Remove the tubes, then cover the surface of the internal reflector with LEDs. The heat is spread out, the whole string can be in series, and when one cartridge fails, the small red LED shows you which one to replace. This solves most (if not all) of the issues with LED lights. Old fixtures could even be retrofitted with this solution without requiring complete replacement of the fixture. With a more expensive "ballast," dimming could be supported for daylighting or load shedding. As I've mentioned before, however, phase-cut dimming is not a good idea. Either powerline-based data communication or wireless control (insert shameless plug for Illumra products here-remember I work for them :-) is the only good option for dimming the lights. The extra cost (in the bulb/ballast/fixture) to support phase cut dimming (just so you can use your old "standard" wall box dimmer) is not worth it.
Two unrelated notes:
One, I've been adding new features recently to the firmware in many of the Illumra dimmers and load controllers. From day one, we've always tried to select default operating modes that are the most convenient for the users of the products. At the same time, while they save energy as much as possible, we don't want their operation to be intrusive. For example, if a receiver is set up to turn off the lights when the space has been unoccupied for a while, for a time, after the lights turn off, if occupancy is detected, they turn back on. However, California Title 24 (which includes regulations updated in 2005 for how these devices must operate) doesn't allow automatic turn-on when you enter a room. We're making Title 24 compliance the standard operating mode for our receivers, even though it's potentially more intrusive (meaning you must turn on the lights manually when you first enter the room). It's been a tough decision, but since an automatic-on mode is available, we'll still support modes that require less intervention. Perhaps if you are ever irritated by a light that could turn on automatically, but doesn't, you can remember that you may be saving a little more energy (and money) that way.
Two, while I won't be there personally, if you're in New York next week, drop by our booth at the Lightfair tradeshow. Illumra products will be shown in one part of the EnOcean Alliance booth, as well as integrated into a number of products under various brand names throughout the show.
Friday, April 17, 2009
Luminous Efficiency of LEDs vs. CFL
There is a lot of misinformation about the efficiency of LED lighting. Much of the information out there is not about what LEDs can do today, but rather what they are working toward. In the end, what we all care about, when trying to save energy, is Luminous Efficacy, which is the efficiency of the conversion of electricity into usable light. It's specified in Lumens per Watt.
A good quality fluorescent bulb with an electronic ballast provides on the order of 100 lumens per watt. If it's a dimmable fluorescent, that number can go down quite a bit when dimmed to low levels (down, you ask? Yes, there is a fixed amount of power to run the ballast that doesn't change with dim level, which isn't converted into light). A compact fluorescent is usually in the 50 to 80 lumens per watt, I understand. Only the most exotic prototypes in a lab environment an beat this with LED sources. Most of them are well below what a compact fluorescent can do.
Of course we all want a better light source, so enormous amounts of money (both private and public) is being poured into LED research. I'm sure, in time, the efficacy will improve. I found this nice article about the fundamental sources of heat produced in LEDs, which gives a good outline of where the waste energy is going, but it stops short of giving efficacy numbers. The biggest challenge today, I think, is thermal management. If the LEDs are run at too high a temperature, they will not live up to their promise of long life. CFLs suffer the same problem, and in the wrong kind of fixture they only last a few months instead of the many years they are capable of.
The best way to save energy, now and always, is to turn off lighting that is not needed. While I still train my children to turn off the lights when they are not in the room, they still forget often enough, and the motion detectors I've set up take care of the rest.
A good quality fluorescent bulb with an electronic ballast provides on the order of 100 lumens per watt. If it's a dimmable fluorescent, that number can go down quite a bit when dimmed to low levels (down, you ask? Yes, there is a fixed amount of power to run the ballast that doesn't change with dim level, which isn't converted into light). A compact fluorescent is usually in the 50 to 80 lumens per watt, I understand. Only the most exotic prototypes in a lab environment an beat this with LED sources. Most of them are well below what a compact fluorescent can do.
Of course we all want a better light source, so enormous amounts of money (both private and public) is being poured into LED research. I'm sure, in time, the efficacy will improve. I found this nice article about the fundamental sources of heat produced in LEDs, which gives a good outline of where the waste energy is going, but it stops short of giving efficacy numbers. The biggest challenge today, I think, is thermal management. If the LEDs are run at too high a temperature, they will not live up to their promise of long life. CFLs suffer the same problem, and in the wrong kind of fixture they only last a few months instead of the many years they are capable of.
The best way to save energy, now and always, is to turn off lighting that is not needed. While I still train my children to turn off the lights when they are not in the room, they still forget often enough, and the motion detectors I've set up take care of the rest.
Wednesday, April 8, 2009
CFL power quality
Long-term (assuming that CFL bulbs become a substantial percentage of the load on our power grid) the cheap power supplies that are built in most compact fluorescent bulbs will create power quality problems. See this article for some details.
While I agree that it's a problem, having designed power supplies like them, I would assert that it's already been a problem historically, and perhaps is presently, too. The harmonic content generated when a rectifier sits directly on the AC power line, connected to capacitors on the DC side, is pretty nasty. Perhaps counter-intuitively for those of you with an electronics background, the noise becomes worse if you use more capacitance after the rectifier. Think of it this way: a larger capacitor doesn't droop as much between power cycles, so the recharge occurs over a smaller piece of the power line cycle, making a shorter (but higher-amplitude) spike of current. During the remaining power cycle, little or no current is drawn.
While this doesn't represent the traditional inductive or capacitive load (a simple phase lead or lag of current) it's a power quality problem. Capacitor banks on the utility distribution lines will not solve the problem. In the end, the power supplies at the end of the service line must be improved.
As an example of this problem, see this image below of the AC waveform at my house. Compared to a pure sine wave, the peak is significantly clipped. I believe it's due to non-power-factor-corrected power supplies that are in use throughout my neighborhood (and I think the same is true of most parts of the power grid).
While I agree that it's a problem, having designed power supplies like them, I would assert that it's already been a problem historically, and perhaps is presently, too. The harmonic content generated when a rectifier sits directly on the AC power line, connected to capacitors on the DC side, is pretty nasty. Perhaps counter-intuitively for those of you with an electronics background, the noise becomes worse if you use more capacitance after the rectifier. Think of it this way: a larger capacitor doesn't droop as much between power cycles, so the recharge occurs over a smaller piece of the power line cycle, making a shorter (but higher-amplitude) spike of current. During the remaining power cycle, little or no current is drawn.
While this doesn't represent the traditional inductive or capacitive load (a simple phase lead or lag of current) it's a power quality problem. Capacitor banks on the utility distribution lines will not solve the problem. In the end, the power supplies at the end of the service line must be improved.
As an example of this problem, see this image below of the AC waveform at my house. Compared to a pure sine wave, the peak is significantly clipped. I believe it's due to non-power-factor-corrected power supplies that are in use throughout my neighborhood (and I think the same is true of most parts of the power grid).
Wednesday, March 18, 2009
Sustainability and why dimming your lights may not save...
I ran across a series of interesting articles on "sustainability" today. I'm trying to figure out if people are finally joining the sustainability movement because it's becoming more mainstream, or if they really think it's a good idea. Perhaps the higher cost of energy (recently) has been pushing people to save money. Maybe the economic downturn is hitting people so they're trying to save money everywhere they can.
In any case, the ILLUMRA philosophy still applies: saving energy (for any reason) by automating and controlling devices that use energy. Decades ago it only mattered that the lights worked, the cost of operating them was small in comparison with the light bulb itself (or so everyone assumed). Of course most of the products sold by ILLUMRA (the company, as opposed to this, the blog) involve energy harvesting in one way or another, which ultimately saves wiring, batteries, or both.
In any case, here are links to the articles:
Survey: Americans favor Sustainable Engineering and Manufacturing
Energy cost savings through load shedding (and load balancing)
The power factor issue in the second item will be, I believe, a bigger issue in the future. I've been recently working over ideas for large-scale (building-wide) LED lighting systems. It's critical that the power supplies (ballasts) for the LED lights include power factor correction, and therefore act as "nice" loads on the grid. This will avoid the kinds of noise-induced power quality issues that often occur in large manufacturing environments. Years ago, power supplies in all PCs were not power factor corrected, and contributed to power quality problems (including neutral heating) in office buildings. If someone goes a "too-cheap" route when converting their lighting, they could create as many problems as they solve.
One reason this is so important: Dimmable fluorescents are a nice way to introduce some energy savings (and load-shed capacity) to a building. However, if you use ballasts that support phase-cut dimming on their line inputs (as opposed to 0-10V low voltage control dimming) then the effective power factor will degrade. If a whole office building used this technique to load-shed during a high-demand time-of-day, the net effect may actually increase the electric bill of the facility (because of the power factor and demand charges outlined in the second article above). It's important that while phase-cut dimming is a nice feature on a dimmable ballast (fluorescent or LED) it's not a good way to control a large number of ballasts. A 0-10V solution (wired or wireless) is the best way to go.
In any case, the ILLUMRA philosophy still applies: saving energy (for any reason) by automating and controlling devices that use energy. Decades ago it only mattered that the lights worked, the cost of operating them was small in comparison with the light bulb itself (or so everyone assumed). Of course most of the products sold by ILLUMRA (the company, as opposed to this, the blog) involve energy harvesting in one way or another, which ultimately saves wiring, batteries, or both.
In any case, here are links to the articles:
Survey: Americans favor Sustainable Engineering and Manufacturing
Energy cost savings through load shedding (and load balancing)
The power factor issue in the second item will be, I believe, a bigger issue in the future. I've been recently working over ideas for large-scale (building-wide) LED lighting systems. It's critical that the power supplies (ballasts) for the LED lights include power factor correction, and therefore act as "nice" loads on the grid. This will avoid the kinds of noise-induced power quality issues that often occur in large manufacturing environments. Years ago, power supplies in all PCs were not power factor corrected, and contributed to power quality problems (including neutral heating) in office buildings. If someone goes a "too-cheap" route when converting their lighting, they could create as many problems as they solve.
One reason this is so important: Dimmable fluorescents are a nice way to introduce some energy savings (and load-shed capacity) to a building. However, if you use ballasts that support phase-cut dimming on their line inputs (as opposed to 0-10V low voltage control dimming) then the effective power factor will degrade. If a whole office building used this technique to load-shed during a high-demand time-of-day, the net effect may actually increase the electric bill of the facility (because of the power factor and demand charges outlined in the second article above). It's important that while phase-cut dimming is a nice feature on a dimmable ballast (fluorescent or LED) it's not a good way to control a large number of ballasts. A 0-10V solution (wired or wireless) is the best way to go.
Friday, February 27, 2009
Energy Harvesting - not ready for prime time?
Nice brief summary article relating to energy harvesting technologies:
http://www.greensupplyline.com/214301888
I've got mixed feelings about his assertion that energy harvesting isn't ready for "prime time" yet, though. While I will agree that it's not close to being a technology that fits every application yet, there are certainly some nice niches that fit well.
For example, there are a lot of buildings that can be retrofitted with energy saving lighting controls (California's Title 24 regulation in particular) but the installation cost is high in order to route wiring for occupancy sensors in the room (or even worse, installing a sensor on every fixture). In this case, a wireless, battery-free, energy harvesting motion detector (other manufacturers with the same concept: 1, 2) is a perfect fit. While the equipment cost is higher than that of a wired system, the installation cost is much lower, possibly less expensive overall, but certainly competitive. The sensor harvests solar energy, stores it (enough to run for two days or so in darkness) and operates the occupancy sensor and the radio transmitter.
In contrast, and ultrasonic sensor uses thousands of times more energy, so to make an energy harvesting vacancy sensor (or occupancy sensor) would require a very large solar panel, enough to make it impractical. So much energy is required, in fact, that it would make a lot of sense to turn the sensor off when the lights are off (unless automatic on is required -- CA Title 24 doesn't allow for that) or at least reduce it's operating duty cycle.
On a related note, there is a movement to revive magnetic coupling to charge cell phones, laptops, and the like. Inductive power coupling is nothing new, it's been around for years. I have a waterproof cordless phone that charges without any electrical contacts, I understand that many electric toothbrushes recharge the same way. In much the same way that Apple made touchscreens new and exciting with the iPod Touch and the iPhone, companies are going to revive magnetic coupling so you can put your laptop on a special pad on (or embedded in) a table or desk and charge without a cord.
While it's convenient, the relatively low efficiency of this power transfer method runs counter to some of the goals of the green movement. On the upside, however, the stray fields from these devices may provide a new mechanism for energy harvesters. Adding a small magnetic pickup coil to an energy harvesting device may, in the future, provide sufficient energy to run these sensors without the need for a solar cell, mechanical, or thermal harvester.
http://www.greensupplyline.com/214301888
I've got mixed feelings about his assertion that energy harvesting isn't ready for "prime time" yet, though. While I will agree that it's not close to being a technology that fits every application yet, there are certainly some nice niches that fit well.
For example, there are a lot of buildings that can be retrofitted with energy saving lighting controls (California's Title 24 regulation in particular) but the installation cost is high in order to route wiring for occupancy sensors in the room (or even worse, installing a sensor on every fixture). In this case, a wireless, battery-free, energy harvesting motion detector (other manufacturers with the same concept: 1, 2) is a perfect fit. While the equipment cost is higher than that of a wired system, the installation cost is much lower, possibly less expensive overall, but certainly competitive. The sensor harvests solar energy, stores it (enough to run for two days or so in darkness) and operates the occupancy sensor and the radio transmitter.
In contrast, and ultrasonic sensor uses thousands of times more energy, so to make an energy harvesting vacancy sensor (or occupancy sensor) would require a very large solar panel, enough to make it impractical. So much energy is required, in fact, that it would make a lot of sense to turn the sensor off when the lights are off (unless automatic on is required -- CA Title 24 doesn't allow for that) or at least reduce it's operating duty cycle.
On a related note, there is a movement to revive magnetic coupling to charge cell phones, laptops, and the like. Inductive power coupling is nothing new, it's been around for years. I have a waterproof cordless phone that charges without any electrical contacts, I understand that many electric toothbrushes recharge the same way. In much the same way that Apple made touchscreens new and exciting with the iPod Touch and the iPhone, companies are going to revive magnetic coupling so you can put your laptop on a special pad on (or embedded in) a table or desk and charge without a cord.
While it's convenient, the relatively low efficiency of this power transfer method runs counter to some of the goals of the green movement. On the upside, however, the stray fields from these devices may provide a new mechanism for energy harvesters. Adding a small magnetic pickup coil to an energy harvesting device may, in the future, provide sufficient energy to run these sensors without the need for a solar cell, mechanical, or thermal harvester.
Monday, February 9, 2009
LED vs. CFL vs. Incandescent
This article I read on edn.com, while it contains nothing I haven't read elsewhere, is a nice summary of the whole migration toward LED lighting. I hope to see LED lights that approach the efficacy (efficiency in terms of lumens per watt) of a good fluorescent light (around 100 lumens per watt). One named in the article was getting closer (about 80) and I've heard of laboratory tests of prototypes that are in the neighborhood of 150 (yes!).
I still want to see an intelligent way to retrofit existing dimming bulbs with dimmable CFL and LED fixtures. I think a bidirectional communication protocol between the bulb and the dimmer might be a way to do it, perhaps over the existing power line. The problem with that method is the extra cost, complexity, and reliability of adding that hardware to the bulbs and the dimmers. A dimmer would probably need to detect the connected load, and either use traditional dimming (for regular bulbs) or leave the power fully on and communicate the dim level, letting the ballast at the load control the brightness.
Perhaps the communication can occur by doing phase cutting, much like regular dimming, but use a 95% brightness level for one digital level (zero or one) and 100% brightness for the other value, and use, in effect, a serial data stream over the power line.
Long term, however, low or medium voltage DC power to the lighting loads, with digital control at the point of load, would be more efficient and have fewer points of failure than the current methods.
Just a few random thoughts. I hope to come up with a more coherent post in the near future. It's been a very busy few weeks, so I haven't been able to write a more organized, thoughful post than this.
I still want to see an intelligent way to retrofit existing dimming bulbs with dimmable CFL and LED fixtures. I think a bidirectional communication protocol between the bulb and the dimmer might be a way to do it, perhaps over the existing power line. The problem with that method is the extra cost, complexity, and reliability of adding that hardware to the bulbs and the dimmers. A dimmer would probably need to detect the connected load, and either use traditional dimming (for regular bulbs) or leave the power fully on and communicate the dim level, letting the ballast at the load control the brightness.
Perhaps the communication can occur by doing phase cutting, much like regular dimming, but use a 95% brightness level for one digital level (zero or one) and 100% brightness for the other value, and use, in effect, a serial data stream over the power line.
Long term, however, low or medium voltage DC power to the lighting loads, with digital control at the point of load, would be more efficient and have fewer points of failure than the current methods.
Just a few random thoughts. I hope to come up with a more coherent post in the near future. It's been a very busy few weeks, so I haven't been able to write a more organized, thoughful post than this.
Subscribe to:
Posts (Atom)