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Posts Tagged ‘efficiency’
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Wednesday, October 7th, 2009LED Lighting, About Efficiency
Wednesday, August 26th, 2009LED lighting offers claims of very high efficiency. Recently I’ve seen claims of over 100 lumens per watt and efficiency of four to five times that of incandescent. First, a refresher on efficiency (and efficacy) for those that need it. The following are link-backs to the previous posts I made regarding efficiency, and they should open up in a new window so you can just close it when you’re done reviewing to get back here.
- How Do I Know What’s Efficient?
- Efficiency Comparison Pitfalls: Age
- Efficiency Comparison Pitfalls: Systems
The problem with trusting efficiency claims from LED manufacturers is based on the complexity of the systems. The initial efficiency measurement is made with a controlled junction temperature of 25˚C and lasts for only a millisecond. These measurements are made of the LEDs themselves and before the LEDs are built into any sort of fixture.
LEDs are sensitive to current. As current increases, the efficiency decreases. Most LEDs used for lighting applications run at around 350 milliamps, or 0.350 amps. Like a fluorescent lamp requires a ballast to control voltage, an LED needs a driver to control the current. And just as a fluorescent ballast decreases the efficiency of a fluorescent lamp, the driver decreases the efficiency of the LED module. At present, the rule of thumb is that you can expect a loss of 10 to 15% efficiency due to the driver. Remember, the LED is an electronic component and the power supplied is connected by an electric component. The driver is the link between them.
LEDs are also sensitive to heat. As the temperature rises above or drops below the testing temperature of 25˚C (which is about 77˚F) the efficiency drops. LEDs are commonly described as not producing much heat, but that is only partially true. The current passing from the circuit board to the diode creates heat, so the heat that is generated comes out the back of the module, not the front. You can touch the front of an LED and it is cool to the touch, but the module itself will be mounted on some sort of heat sink that will be hot. When the initial testing is done it only last a fraction of a second, but in continuous use the efficiency of that heat sink comes into play. Again, the rule of thumb at present is that you can expect a loss of 8 to 10% for thermal management.
Playing even more into that loss of efficiency is sticking an LED module into some sort of fixture housing. You can’t just stick an LED module on your ceiling or wall as a light fixture. (In order to do that your wall and ceilings would have to be made out of circuit boards, so it would look like living inside a computer, which I suppose some people might thing was cool.) The LED module has to go into something, and at present the LED manufacturers and fixture manufacturers are different companies. A fixture manufacturer buys an LED module from someone else and then has to figure out how to deal with the heat and everything else. While the best fixture design possible might maintain that 8 to 10% loss in efficiency due to heat, a poor fixture design can increase that loss even more.
LEDs are also directional sources. If you take a regular incandescent light bulb and stick it in a bare socket, the light travels in all directions and lights up the whole room. If you take a halogen PAR lamp and stick it in a base socket, it lights up mostly in one direction like a cone of light. The LED is similar to the PAR lamp although it typically has a tighter cone of light. To use an LED to light up a room there has to be some method of optically controlling the light distribution. At present, the rule of thumb is that you can expect another 10 to 15% decrease in efficiency due to whatever method is used for optical control.
Aside: I’ve used a halogen PAR lamp as an example of a directional light source since most people are familiar with that type of bulb. Keep in mind that a PAR lamp is a combination of a light source an optical control system. The filament inside the lamp is omni-directional, just like a regular light bulb, but the glass and metal envelope surrounding it control the light to make it directional. The final result is less efficient than if we just uncovered the bare filament inside the bulb, but since we’ve packaged the whole thing as a lamp we ignore that loss and just use the efficiency of the entire unit for calculations. Keep in mind we’ve had a century of experience now at controlling omni-directional light, which is what we get from all incandescent and fluorescent sources. LEDs are the first fundamentally directional sources we’ve developed so we are still fairly new at utilizing the light generation.
So if we add up the efficiency losses from the driver, heat, and optical design, we’ve already lost 28 to 40% of the LEDs efficiency just by taking the thing out of the laboratory and trying to stick in into a lighting fixture (or flashlight, or whatever).
There are other losses in efficiency that are harder to illustrate. LEDs typically have a very high color temperature. Decreasing that color temperature to something that would be more appropriate to general lighting decreases the efficiency. LEDs emit light in specific regions of the color spectrum based on the materials used, which is similar to the issues regarding fluorescent lighting. When efforts are made to increase the color rendition, similar to increasing the CRI of a fluorescent lamp, the efficiency decreases.
The take-away here is that you can’t just look at the efficiency of the LED module and make an assumption about the efficiency of the LED light. The only way to determine the efficiency is to look at the efficacy of the entire system after it is designed and potentially installed. That why if you review my postings about the new lighting requirements for California they specify that the efficiency of LED lighting has be done based on the entire LED module/driver system, not just the lamping. The efficiency of the lamp all that is required for incandescent or fluorescent lighting options.
California Lighting, Final Thoughts
Wednesday, July 22nd, 2009All in all, the California Title 24 legislation is pretty progressive. With regard to lighting, it is really focused toward making you think about the lighting in your home. You really have two primary approaches toward lighting your living space: either committing fully to fluorescent lighting or using dimmers throughout your home for energy savings. The state is also clearly looking forward to LED lighting, but frankly the industry isn’t ready to support that yet. However, the rate of growth is so strong it will only be a few more years before that changes.
If you commit to fluorescent lighting remember to consider the color temperature and color rendering index of each lamp. Right now people aren’t accustomed to the way everything appears under fluorescents, but I think in a generation the quality of fluorescent lighting will become our new “normal.” With technological advances the fluorescent and LED sources will improve and either the manufacturers will make them more like natural light or (more likely) we’ll just grow to accept the spectral profiles of those sources.
However, if you aren’t ready to make that leap yet you can use dimming systems. I think everyone should use dimming in their homes even if they don’t care at all about energy efficiency, since I believe the quality of life benefits shouldn’t be ignored.
And instead of just using local dimmers, hopefully this will stimulate the use of wider-ranging lighting systems. System that enable you to program lighting for entire rooms rather than just adjusting each circuit. There are countless options out there so don’t feel limited by the adoption of more stringent energy efficiency standards as they progress from the west coast eastward.
California Lighting, Special Rooms
Monday, July 20th, 2009Special Rooms-Kitchen:
The biggest and most complex part of the lighting section of California’s Title 24 is with regard to kitchen lighting. You are allowed to use a combination of high and low efficacy fixtures in the kitchen because the state considers the visual requirements in the kitchen to be so much more complex than in the rest of the home.
You can use low efficacy fixtures (only in the kitchen) with a combined wattage not to exceed the combined wattage of high efficacy fixtures also in the kitchen. That means if you install 150 watts of high efficacy fluorescent lighting in the kitchen you are also allowed to install up to 150 watts of low efficacy incandescent, halogen, or low-voltage lighting.
Lighting built into cabinets is excluded because it has its own rules, but those built-ins must only light the inside of the cabinet. Lighting attached to the outside of the cabinets does not count as cabinet lighting, but must be included as part of the kitchen wattage calculation. The same goes if you have lighting inside your cabinet but it is designed to light surfaces outside of the cabinet. That is, you can’t install one of the low-voltage striplights that has little MR-16 attachments to point onto your counters to try to get around the kitchen wattage restrictions.
The high efficacy and low efficacy lighting in the kitchen must be controlled separately. (Actually, that is true everywhere, but since you can’t use low efficacy fixtures unless they are dimmed the distinction is a little pointless. You can’t combine different source types on a dimmer, so you couldn’t dim both incandescent and fluorescent fixtures on one control. I guess the only way to mix would be if all of them were on a vacancy sensor, but you shouldn’t be mixing fixture types in any room in which you want to use vacancy sensors anyway.)
To calculate the wattage of the low efficacy fixtures you must use the highest wattage allowed by the fixture. That means you can’t “save” by putting a smaller light bulb in the fixture, say a 60 watt bulb in a fixture that can take up to 100 watts. If you are using low-voltage fixtures you have to use the input wattage of the transformer, which is most likely going to be higher than the wattage of the lamp or lamps.
If you want to use track lighting in your kitchen there are a number of different ways to calculate the wattage against your allowance, but the easiest is just to use 45 watts per foot of track, unless the actual lamping is greater. Yep, a three foot section of track over your island counts as 135 watts, even if you just put two dinky 20 watt pendants on the track. If instead you put three 75 watt incandescent lamps you would have to use the higher combined wattage of 225.
The state has also figured you might try to get around the restriction by running your wiring to boxes and then not hooking up any fixture until after the inspection is complete. So each electrical box either covered by a blank plate or where there isn’t any electrical equipment hooked up counts as 180 watts of low efficacy power toward your allotment. Actually, this is often done innocently when you are going to install a ceiling fan but it hasn’t been picked out yet. The electrician runs the wires to a box that will someday support the fan for you, but he may be done and off the job before the final fan selection is made if you are going to install the fan yourself.
Finally, if you have a kitchen that seamlessly merges into your breakfast nook or any other room you have to be careful with the control wiring. If it looks like a single room the nook will be counted as part of the kitchen unless the lights are controlled by different switches/dimmers/whatever.
Other rooms:
The restrictions for bathrooms, attached and detached garages, laundry rooms,closets, and utility rooms are tighter than for the rest of the home. All the fixtures in all of these rooms must be high efficacy. There are only two exceptions: one, you can use permanently installed low efficacy fixtures if the control is a vacancy sensor; or two, if the closet is less than 70 square feet you can have permanently installed low efficacy fixtures without a vacancy sensor.
Notably missing from the exceptions for these rooms is the exception for using dimmers. As a personal point, I am sorry this is the case since I think that it is pretty important to dim the lights in the bathroom. See my post on dimmers in the bathroom for the reasons why. And if you have dimmed incandescent or halogen fixtures throughout your home I think it is poor design to use dimmed fluorescent in the bathroom.
California Lighting, Overview
Thursday, July 16th, 2009California has recently adopted energy efficiency standards that have a huge impact upon lighting. And since California has been leading the country in energy efficiency standards I thought I’d write up a quick summary of what homeowners ought to know about the changes to residential lighting since it is just a matter of time before similar rules spread to the rest of the country. Note that there are a couple adoption dates that we haven’t reached yet, so the entire Title 24 code isn’t in effect as of right now, but we may as well look to the future.
First of all, the new rules apply to all new residences and other projects that require a permit, so chances are you’re going to have to comply. Portable lighting, such as table and floor lamps, are not covered by the changes. However, all permanent lighting is covered and that basically includes anything attached to a surface. So you can’t stick a lighting track on the ceiling but control it by a cord plugged into an outlet. Lighting installed in furniture like cabinets or bath vanities is included. The big exception to this is lighting that is built into appliances, such as microwaves, refrigerators or stove exhaust hoods.
The idea is to divide lighting fixtures into high efficacy and low efficacy groups. You can install all the high efficacy fixtures you want anywhere you want. (Interestingly, to divide the fixtures into high and low efficacy the rules use just the lamp efficiency, rather than the actual fixture efficacy. Remember the efficiency/efficacy post?) To determine if a fixture is high efficacy it must comply with the following lumens per watt limits.
- If the fixture’s lamp is 5 watts or less, it must get at least 30 lumens per watt.
- If the fixture’s lamp is up to 15 watts, it must get at least 40 lumens per watt.
- If the fixture’s lamp is up to 40 watts, it must get at least 50 lumens per watt.
- If the fixture’s lamp is over 40 watts, it must get at least 60 lumens per watt.
(However, the method to determine the lumens per watt of LED fixtures has some restrictions so you can’t use the LPW of the LED module. You have to use the input power of the LED driver, but then it must also comply with the same LPW restrictions as above. You do NOT have to take the ballast for fluorescent lamps into account.)
Anything that doesn’t meet the above LPW restrictions is considered a low efficacy fixture.
In addition, there are some things that will automatically classify fixtures as a low efficacy fixture, the most important being that anything with a screw base socket is considered low efficacy. That means all fixtures using the medium or candelabra size socket that all our fixtures in our homes have been using for decades. There are some other things but the screw base socket is the most important. There is an exception for HID lamps with screw base sockets, and a huge section regarding the GU-24 base, but you probably won’t have to be concerned with those details.
Now, once you know what is high efficacy or low efficacy you can figure out what you can install in your home. There is a complex exception for the kitchen, but the basic rule of thumb is that you can only use high efficacy fixtures in your home.
Now, there are exceptions for most of your living areas:
- Low efficacy fixtures may be used if the circuit is controlled by a “vacancy sensor.” This is not the same as an occupancy sensor! A vacancy sensor is defined by the state as a control that can only be turned on manually and will automatically turn itself off after a preset time of 30 minutes or less unless it detects that the room is occupied or if the control is turned off manually. This explicitly excludes controls that turn on automatically, which is how occupancy sensors typically work. Also, if the control has a switch or something that allows you to choose if the turn on method is manual or automatic, it does not count.
- Low efficacy fixtures may be used if the circuit is controlled by a dimmer. The dimmer can be one that has several steps instead of a continuous sliding range, however, the dimmer must reduce the energy use by at least 65% at its lowest setting. That means that two-level switches with three settings (off, 1/2, and full on) do not count. Three-level switches which have four settings (off, 1/3, 2/3, and full on) do count. Also, if the dimming circuit can be controlled from multiple locations it must be impossible to bypass the dimmer. The alternate locations can either be remote dimmers or switches that turn the lights either off or to the dimmed level only.
There are exceptions and additions, most notably in the kitchen. However, it’s fairly involved so I’ll address them in the next post.
Residential Fluorescent Lighting
Tuesday, July 14th, 2009So, yesterday I posted a process I might go through to replace a fixture in my home with something more energy efficient. However, it isn’t really what I would do in my own home because I like everything to be dimmed. That includes fluorescents.
A good number of fluorescent and compact fluorescents can be dimmed using dimming ballasts. That does NOT include the self-ballasted CFLs with the screw-in base that you find at the hardware store. GE has come out with a self-ballasted replacement CFL that can be dimmed, and I’m sure others either have or will have soon their own versions. However, these can only be dimmed about 50% before they just turn off. They aren’t worth it.
Instead, I would have to buy separate dimming ballasts and install them myself. I would also have to change out my dimmers to a special versions for fluorescent lighting or perhaps install an interface. Some fluorescent dimming is done using two-wire ballasts, which would be easier to install using existing wiring, but the better dimming is accomplished using three-wire ballasts, which requires a third connection between the dimmer or interface and the ballast.
Fluorescent dimming ballasts typical have a minimum power setting of 1%, 5%, or 10%. For residential use I always recommend using 1% ballasts. This is because reducing the power doesn’t look like the same amount of light reduction. If you dim fluorescents down to a 10% it looks like it has only been dimmed down to about 30%. This just isn’t low enough for use in homes. Instead, using a 1% ballast means the lighting will look like it has been reduced to about 10%.
Efficiency Comparison Pitfalls: Systems
Friday, July 10th, 2009Another pitfall with comparing lamp source efficiency is the entire system’s efficacy.
With incandescent and halogen sources, the wattage on the label is pretty much what you get.
- Technical info, you don’t have to read or understand this: the “what you see is what you get” assumes that the voltage matches. That is, a normal 100 watt light bulb will consume 100 watts at normal household voltage of around 120V. If the voltage is increased, the wattage increases, and if the voltage is decreased the watts consumed also decreases. Some manufacturers use this effect to create longer life and energy savings bulbs; for example, GE sells a 100 watt 130 volt lamp (3,000 hour life) which is labeled for 120 volt use as using 89 watts (8,300 hour life). Of course, the light output also decreases, and it decreases faster than the energy savings: losing 25% of the light output while only saving 11% of the electricity consumption.
Discharge sources, like fluorescent, require some form of control gear to regulate the electricity being consumed. The wattage label on the bulb is not the wattage which will actually be used in the system because the lamps can’t regulate their energy consumption themselves. They require a ballast to do that for them.
Since the ballast is what actually controls the wattage consumption, you have to calculate the efficiency of the system using both the lamp (for the lumen output) and the ballast. Professionals use the term efficacy instead of efficiency to remind themselves that they are dealing with the multipart system rather than just a lamp. So if you compare the efficiency of an incandescent bulb to a fluorescent replacement, you have to make the comparison against the system’s efficacy, not the lamp efficiency.
For the self-ballasted compact fluorescents you pick up at Wal-Mart the comparison is still fairly easy, since the ballast is included as a part of the lamp and the wattage listed on the box is for the ballast. In that regard, you can compare a regular light bulb off the shelf with the CFL next to it. However, if you live somewhere like California, where they have outlawed the use of medium screw based sockets in new construction (emphasis on new), you can’t use a self-ballasted CFL anymore.
Instead, you have to look at the efficacy of the lamp/ballast combination. Different ballasts will have all kinds of different ratings and properties that make reviewing them mind-numbing for the average person who just wants a light bulb. The take away is that the lamp ballast efficacy will be different than the lamp source efficiency. Usually it is less, although sometimes a system can have better efficacy than its lamp’s efficiency.
- Technical info, you don’t have to read or understand this: Ballasts affect the lumen output out the lamps they control separate from the age issue I discussed previously. The affect is known as the “ballast factor,” which is the ratio of what the ballast does to the lamp it is powering versus the fictitious “perfect laboratory ballast” which is used to give the lumens shown on the lamp box. The number is a percentage (real output divided by “perfect” output) and written to two decimals (0.77 or 1.53). You will see ballast factors greater than 100%, accompanied by a wattage higher than the wattage listed for the lamp alone. To determine actual lumen output, you have to multiple the listed lumens by the ballast factor. This new lumen value is what you use to determine the efficacy of the system, along with the ballast’s wattage for that lamp. One ballast may have different ballast factors for different lamps, which will be listed. For easy comparison of ballast factors among different ballasts, there is also a “ballast efficacy factor,” which is the ballast factor divided by the input watts. The higher this BEF the more efficient the lamp/ballast combination, so you can compare ballasts for the same lamp that may have different wattage usage.
An example to demonstrate that you have to look at both the lamp and ballast:
I’m using a 4′ long linear T8 lamp, like you see in a 2′x4′ office fixture that is recessed in a grid ceiling made up of 2′x2′ tiles. To be specific, it is a GE F32T8/SPX35/ECO, which provides 2800 (mean) lumens for 32 watts. My first ballast option is going to be a GE “Residential Grade ProLine” ballast (GE232-120-RES). The lumen output for one lamp is 2,772 (mean lamp lumen times the ballast factor). The system wattage is 32, so the efficacy of the system is 86.6 LPW. I then substitute the “Residential Grade” for a regular “ProLine” ballast (GE232-120-N). The lumen output for one lamp is now 2,632. The system wattage is 36, so the efficacy is now 73.1 LPW. I want to try one more ballast and I choose the “UltraMax Instant Start Multi-Voltage High-Efficiency” because the name sounds cool and highly efficient (GE132MAX-L/ULTRA) The lumen output is now 2,156. The system wattage is 25, so the efficacy is 86.2 LPW.
To choose my ballast, and because I don’t care about how much each one costs for this example, I discount the “ProLine” ballast since it gives me similar output to the “Residential Grade” ballast with less efficacy. Now, I have to choose between the “Residential Grade ProLine” and the “UltraMax.” They have similar efficacies, so I have to choose which I want based on the lumen output. What I haven’t told you yet is that I’m replacing a surface mounted fixture in my home that uses two 75 watt bulbs. The lumen output of the existing fixture that I am trying to match is 2,340, which falls between the 2,772 of the “Residential Grade” ballast and the 2,156 of the “UltraMax.” Rather than decide based on the efficacy or the wattage of each individual ballast I have to select the ballast based on the light output. I decide that I always though the room was a little bit too dark anyway and so I choose the “Residential Grade” ballast. Now, I’ve got a touch more light than before while saving about 75% of the energy, dropping from 150 watts down to just 32!
PS: I’ve written this using fluorescent lighting as the examples, but the same is true for all the gas discharge sources, like metal-halide, high-pressure sodium, etc. High-pressure sodium is an especially efficient light source, although it suffers from all those color temperature and color rendition problems discussed in previous posts.
Efficiency Comparison Pitfalls: Age
Thursday, July 9th, 2009Following up on yesterday’s post, efficiency pitfall number one: age.
An incandescent or halogen light bulb is a fairly closed system. It can be stuck in a socket and what you see is what you get. A 100 watt light bulb is going to be pretty consistent over time. There will be some decrease in the light output as the tungsten filament gets burned up and bits of it get stuck to the inside of the glass envelope, darkening the glass. However, for the most part the lamp will burn out and the filament break before the decrease in light output becomes much of a factor. Tungsten-halogen lamps do slightly better, since the halogen gas inside the bulb makes the tungsten that gets burned off reattach to the filament and basically “recycle” itself, but even though the lamp will last longer and suffer from less darkening it will still break before those changes tip the efficiency equation too much.
Unfortunately, the same cannot be said for the various discharge sources like fluorescent, compact fluorescent, or the various HID types. While a filament does exist in these lamps, the real work of making light is done by the gas discharge. (Check some of my previous posts about fluorescent lighting for a summary of how it works.) The light bulb does not just “burn out,” but instead slowly degrades over time putting out less and less light.
This means that the efficiency of a fluorescent or compact fluorescent decreases over time if you are just using the lumens per watt calculation. For example, the day you install a brand new CFL 26 watt twist self-ballasted lamp you’ll probably get about 1,700 lumens. However, since the output of fluorescent lamps decreases over time, manufacturers also publish the “mean lumens,” which is the lumen output at about 40% of the lifespan of the lamp, which in our example case is 1,365 lumens. So the efficiency has dropped from 65 LPW when brand new to 52 LPW. The lumen output will continue to drop until the lamp reaches the end of its life.
Granted, the lower efficiency of 52 LPW is still much better than the 17.5 LPW of the 100W lamp we’ve replaced (see yesterday’s example). However, remember that you also have 20% less light. So after a while, the new CFL lamp isn’t providing the amount of light you used to have with the old incandescent lamp. This is the point when some people give up and go back to the old lamp, or they add a reading lamp using another incandescent lamp.
Professionals try to counterbalance the lumen decrease by working depreciation factors into the system when they are planning out what lamps to use in a project. We will intentionally over-light a space from day one knowing that eventually the lamps will decrease in output to the level we want for the longer term. The first 100 hours of a CFL or fluorescent is when the decrease is the most rapid, which is called “seasoning.”
As another age related problem, fluorescents don’t necessarily “burn-out” like incandescents and simply stop working. Sometimes, often times, they will just continue to get darker and darker and darker and don’t simply stop turning on. This is why professionals recommend having a maintenance schedule for replacing your fluorescent lamps based on time, not waiting for the lamps to stop working. (What? No one told you this? Yes, if you are going to use CFLs you should keep track of how old the lamps are replace them on a schedule. And yes, it’s much more of a hassle than just waiting for the bulbs to stop working.)
How Do I Know What’s Efficient?
Wednesday, July 8th, 2009I have fielded a variety of questions from people trying to figure out what kind of lighting is more or less efficient than others. Many people understand that lower wattage is better, from a consumption view, but they don’t necessarily feel like they are comparing apples to apples when they try to compare incandescent to compact fluorescent or LED.
The way to determine efficiency of any given source is to figure out how much light you get for the amount of power used. Using the lowest wattage source may not be the most efficient approach if it doesn’t give you enough light and you end up adding more. The lighting industry uses a measurement called Lumens per Watt, or LPW. We take the total lumen output of the source divided by the wattage so we can make direct comparisons.
For example: a regular 100 watt light bulb for a table lamp, with clear glass so you can see through it, will provide about 1,750 lumens (it will say this somewhere on the box). Since it uses 100 watts, you divide 1,750 by 100 and figure out its efficiency is 17.5 LPW. Now you can compare that to a compact fluorescent replacement lamp (with a screw in base for your lamp) and find that it provides about 1,700 lumens for only 26 watts. The CFL lamp has an efficiency of a bit over 65 LPW. Therefore, we can say that the CFL lamp is almost 4 times as efficient as the incandescent.
To provide some general guidance I’ll type up a quick list of some sources and their LPW ranges:
- Standard incandescent bulbs range from around 4 to 20 LPW
- Tungsten-halogen bulbs range from around 18 to 22 LPW
- Low wattage compact fluorescents range from around 20 to 60 LPW.
- High wattage compact fluorescents range from around 50 to 80 LPW.
- Linear fluorescents range from around 65 to 95 LPW.
- LEDs range from around 5 to 40 LPW, although there is so much development of LED sources right now this range is likely to change quickly.
As with everything I write about lighting, there are some caveats. I’ll discuss a few of those in upcoming posts.
