Posts Tagged ‘incandescents’

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Efficiency Comparison Pitfalls: Systems

Friday, July 10th, 2009

Another 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.

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Posted in Fluorescent (and CFL), General Knowledge, Homeowner Tips, Incandescent | 2 Comments »

Efficiency Comparison Pitfalls: Age

Thursday, July 9th, 2009

Following 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.)

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Posted in Fluorescent (and CFL), General Knowledge, Homeowner Tips | 1 Comment »

How Do I Know What’s Efficient?

Wednesday, July 8th, 2009

I 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.

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Posted in Fluorescent (and CFL), General Knowledge, Homeowner Tips, Incandescent, New Tech | 1 Comment »

Color Temperature Basics: What is It?

Wednesday, July 1st, 2009

Color temperature refers to a “black-body radiator.” This is a theoretical object (as in, it doesn’t really exist but we pretend it does because we find that useful) that will absorb all electromagnetic radiation cast upon it; it will reflect or transfer none. Visible light is a small portion of electromagnetic radiation, which you can think of as the stuff coming from the sun that provides light and heat.

When a black body radiator is heated it begins to glow. There’s a cool java applet on the Olympus Microscopy Resource Center website that demonstrates this idea with a picture of a horseshoe. At the lower range it begins by glowing red. Then as it gets hotter it goes through yellow and white phases, eventually shifting into the very bright blue-white range. At any particular color, we refer to the temperature of the blackbody as the “color temperature.” (A note on that java tutorial, the temperature indicated on the scale refers to the tips of the horseshoe. The other colors move down the horseshoe to show that the tips are being heated and the bottom is cooler than the tip. The temperature does not relate to all the colors shown in the image.) The temperature is on the Kelvin scale, which is the same as celsius plus 273. That is, -273˚C is 0 K, 0˚C is 273 K, and 100˚C is 373 K.

For lighting, it is easier to refer to the temperature generating a color than trying to describe the color itself, which changes slowly and is not really part of our language of color. If you are looking at that java applet from Olympus, try to describe the difference between the color of the horseshoe tips at 2700K, 3000K, and 3200K. You’ll quickly realize why referring to a color temperature is easier.

A bit of confusing terminology, however, is that we refer to red the red side as “warm” and the blue side as “cool.” This is based on our traditional color associations of red and blue. It can be confusing because the bluer tint comes as you increase the temperature. Hence, you may hear people refer to “raising” the color temperature to “cool” the light source.

The filament of a regular incandescent lamp is not a true black-body, but it does go through the same color process as it is heated. That’s why when you put a regular lightbulb on a dimmer it shifts toward the red as you dim it down: it’s the horseshoe in reverse. Therefore, if you’re looking at incandescent lightbulbs color temperature isn’t a very useful metric. Regular and halogen lamps at full power usually end up around 2700K to 3050K, and that can be changed by adjusting the voltage. The real purpose of discussing color temperature is for fluorescent lamps, which I’ll get to tomorrow.

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Installing All Those Dimmers!

Monday, June 22nd, 2009

I realized that last week did a good job covering the basics of how to use dimmers in the home, but not about the doing-it-yourself part. You don’t need to hire someone to put dimmers in your home.

From the safety perspective, find the breaker in your panel that controls the power to the light you want to dim and turn it off. With cellphones and cheap two-way radios, you probably don’t even need to yell across the house anymore!

The only tool you’ll need is a screwdriver. The dimmer will use Phillips head screws, but your faceplate may be attached with a standard slotted screw if the home is older. Keep the old screws that attach the faceplate to the box in the wall, but the dimmer will probably have new screws for the dimmer.

The dimmer will include instructions that has pictures as well as text in english and spanish (for the most part). The key is to keep track of the wires that were already attached to the switch! There will most likely be a black and a white wire–or two black wires–connected to the switch, and you just connect the black and white wires on the dimmer to the wires in the wall. Truth be told, it doesn’t matter which is which.

The dimmer package will also contain a couple wire nuts to attach the wires. Some dimmers have holes that you can just shove the wires into for a solid connection, but if not use the wire nuts. Twist the two wires together like a twisty-tie, but it doesn’t have to be real tight. Then just twist the wire nut on, just like a screw-driver (right-makes-tight).

The dimmer will also have a green wire for the ground. There probably won’t be a green wire in the box to connect it to, but it can be attached to the bare metal of the box.

Finally, when you are totally done, check to make sure you didn’t install the dimmer upside down! The slider or rocker should make the lights brighter when you move or press UP and lower when you press DOWN. If the dimmer includes a toggle, up is on and down is off. For a rotary style dimmer it doesn’t matter. Some dimmers have the name of the manufacturer somewhere on the face, which is an easy way to make sure it’s not upside down before turning the power back on.

(Aside, dimmers for three-way switching are more complex and not covered here. A three-way switch is where you can turn the lights on and off from two locations. A four-way switch is where you can turn the lights on and off from three or more locations.)

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Dimmers Throughout the Home

Friday, June 19th, 2009

Lastly, all the others places in the home are when most people start with dimmers instead of ending with them. The dining room, living room, family room, etc. are good places to create the warm family home most people enjoy. Those are often the first places people think to install dimmers since they think of those areas as more “public.” I agree, and since those rooms get used so much they are great places to install dimmers. But if you can’t afford or want to buy dimmers for every room in your house you should leave these rooms until the next round of dimmers and just focus on the rooms discussed in the last few posts.

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Dimmers in the Kitchen

Thursday, June 18th, 2009

The kitchen is an odd sort of place when it comes to dimming. You need to have lots of light for preparing meals, so it would seem to be a place you could skip. However, the kitchen is also a place where many people tend to congregate. To that end, your dimmer will receive much more of a workout, but you’ll end up finding you use it all the time. It becomes a more comfortable gathering place when dimmed, and you’ll find yourself only cracking it up to full to prepare a big meal. Most of the time it will be dimmed down some.

Note that some newer homes have fluorescent lights installed in the kitchen to really pump up the light levels for cooking. If you have a fluorescent light in the kitchen, you’ll need to refer to my postings about fluorescent dimming, which I haven’t written yet. Be on the lookout.

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Dimmers in the Home

Monday, June 15th, 2009

Over the next few days I’ll give some tips for using dimmers in your home. I always recommend people replace their switches with dimmers. It is one of the quickest, easiest, and cheapest ways to improve your lighting environment. Low cost dimmers are available in hardware stores and big-box supply centers (Home Depot, Lowe’s, etc.) all over the country.

Some quick info:

  • Dimming your incandescent loads 10% can save you 10% electricity and can make the bulbs last twice as long.
  • Dimming 50% saves about 40% electricity and can make the bulbs last 20 times longer!
  • Dimming incandescents shifts the color toward the red end, which most people perceive as warmer and more comfortable.
  • Dimming can help with your sleep patterns.

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The Sad News

Friday, June 5th, 2009

Although the two tips posted a couple days ago are quick and easy to do, they aren’t going to provide you with the savings you’ll get from other, more comprehensive methods. Also, your room won’t be as bright as before. The amount of light created by a regular light bulb is directly related to how much power it is using, so reducing the power will reduce the light. However, most of the time a reduction of around 8% won’t be noticeable. However, if you’re using them in a single lamp fixture that is the only source in an entire room you might notice the difference. Or, you may not want to change the lamp in your reading light, but it is a start.

You also won’t get anywhere close to the savings you would get from switching to compact fluorescents. However, you also don’t have to make the lifestyle changes associated with switching to compact fluorescents either. Using compact fluorescent properly involves understanding color and daytime versus nighttime usage. I believe that rampant misapplication of CFL lamps is the reason they haven’t caught on as quickly as their proponents would like. However, in a future blog I’ll discuss ways you can use CFLs properly to improve your life.

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The Reasons for the Savings

Thursday, June 4th, 2009

Yesterday I posted two tips for saving power. The reasons these methods work are a bit technical, but I’ll post the short version just for interest.

  1. Wattage is proportional to the voltage supplied to the lamp and the resistance within the lamp. The power company supplies your voltage, and the lamp manufacturer supplies the resistance. Homes in the US are nominally supposed to have 120 volts supplied at outlets and in built-in lights, although the actual voltage will vary for all kinds of technical reasons. You’ll also see labels listing voltages as a range, such as 110-120V, or as an intermediate number, such as 115V. When you use a lamp that is designed for 130V the manufacturer has decreased the resistance slightly in order to provide the labeled wattage assuming 130V. If you give that lamp less voltage, the wattage is also reduced because the resistance has already been reduced. How much is saved? I’ll round it off to about 8%. Also, the bulb will last longer.
  2. The reason dimmers work at saving electricity is basically the same idea. If you run a cheap dimmer at full, it isn’t really giving you full power. The dimmer creates a cap that is less than full. So, instead of 100%, full power is only 94%. That number is only an example, the actual number will differ based on all kinds of things. Even if you never use the dimmer to dim the lights, they will still be using less energy. Although, if you do dim the lights, you’ll get even more savings. Dimming a light 50% will save 40% power and can make a light bulb last 10 times as long as normal!

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