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Color Temperature Basics: Fluorescents

Thursday, July 2nd, 2009

The real meat of the color temperature discussion is with regards to fluorescent and HID (high intensity discharge) sources. Color temperature is tricky for fluorescents because it is based on heating the black-body object to get a color. However, fluorescent sources do not have an object to heat since there is no (functional) filament. Instead, it is a gas discharge process, so color temperature doesn’t really apply. Instead, we use the CCT, or “correlated color temperature.” This is just an approximation of the color temperature the manufacturer is trying to achieve with their mix of phosphors inside the lamp.

The reason CCT is important is because there are so many different phosphor mixes that can be used. Unlike incandescent lamps, there is a wide range of mixes and each mix, relating to a CCT, establishes what we see as “white.” It is this establishment of “white” that makes any and all of this matter.

By using a different phosphor mix, we make white objects appear either warm or cool, based on the (correlated) color temperature of the light source. All other objects, from artwork to skin color, reflects the same “bias” toward the color we have established as white light. This is why early adoption of fluorescent office lighting was so painful. The phosphor mix and color temperature of the light was shifted so far toward the higher, cool end of the lighting range people didn’t like the way things looked. There were other problems, but the main thing most people took away from the experience was an association of fluorescent lighting being “cold.”

However, we could just as easily make our fluorescent lighting “warm” by using lamps with a CCT with a lower number. For example, you could use lamps with a CCT of 2700 to try to match the incandescent lamps you are used to having in the home. In my experience, most people don’t like a fluorescent lamp with a CCT of 2700K either, since it doesn’t look like a regular incandescent lamp with a color temperature of 2700K. That’s part of the “correlated” aspect, and there is also some color rendering issues which I’ll discuss in following posts.

The trick to good fluorescent and compact fluorescent lighting is finding the CCT you like for any particular use. In more residential settings, a 3000K lamp may be preferred, whereas in an office or kitchen 3500K may be better. You can’t just pick one and use it for everything, although that would be preferable to not picking at all and just installing whatever shows up. Selecting the right color temperature is a part of the lighting design process.

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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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Color Temperature Basics: Why Should You Care?

Tuesday, June 30th, 2009

I mentioned during the introduction to fluorescents that I would have follow-up posts about color temperature and CRI (color rendering index). I’m going to kick this off with color temperature and an explanation of why anyone would care about it.

relative-color-2One of the biggest problems with artificial lighting is that our eye and brain determine a lot of color information by comparison instead of some sort of mental color wheel. I’ve stuck an image file into this post to provide an example. The image to the right is made up of exactly 3 colors, but the purple color appears to be either a lighter or darker purple depending upon whether the adjacent color is the blue or the pinkish color. Also, the purple bar that runs all across the middle seems to change color from one side to the other.

The issue for artificial lighting is that as we look around us, our eye spots the brightest source of light and our brain “sets” that as white light. We are mentally doing the opposite of the what my sample image shows: instead of using relativity of colors to “see” either bright or darker versions of purple when the purple is actually the same, we are using relativity of colors to see different versions of “white” and then perceiving that as always the same “white.”

For the common user, a lightbulb (unless a specialty colored lamp) is going to be perceived as white. For the professional, we know that different sources are giving us different whites and we need a way to document the differences. We do that by specifying the “color temperature” of the source.

For the next post, I’ll explain what color temperature actually is and how we come up with the numbers.

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Full-Spectrum, Outside Evidence

Monday, June 29th, 2009

No one has complained, but my rigorous academic training has been nagging at my conscience about  not offering citations. Even though it is just my blog, and I am offering advice based on my experience and expertise, I suppose I should offer evidence that I am not just making this stuff up.

A good place to start is the National Lighting Product Information Program, which was established by the Lighting Research Center, which is a manufacturer independent organization backed by the Rensselaer Polytechnic Institute. They have an article about full-spectrum lighting from which I gathered some of the numbers in my previous posts, like the white paper study. That article is a full scholarly work so it is properly cited.

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Last Full-Spectrum Post, I Promise

Monday, June 29th, 2009

I have just a couple more points to make about full-spectrum lamps.

  • They are more expensive. Since “full-spectrum” lighting is a marketing term, you should expect it to be an attempt to get you to pay more for a light bulb. There are reasons to pay more for a light bulb, such as increased efficiency or better color rendition, but paying more for a “full-spectrum” lamp should be approached with caution. You can sometimes get the exact same spectral distribution with greater efficiency from a non-full-spectrum source.
  • They are only worth it if they make you feel better. Some people will just like them. If that is you, and you don’t mind the cost, go ahead and use them. The increased UV isn’t too bad (remember: 8 hours of full-spectrum lighting to equal UVB of 1 minute of sunlight).
  • (A follow-up claim) Full-spectrum can make your whites whiter and paper brighter: This is slightly true, as you can increase the luminance about 1.7 to 2.3% of a piece of white paper or white cloth treated with whitening agents, but at the cost of 30 to 40% less efficacy.
  • Generally speaking, full-spectrum sources are less efficient than the standard version of the same thing. When making a choice, I recommend using the more energy efficient lamp.

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Full-Spectrum Lighting Health Claims

Friday, June 26th, 2009

I realized there are a couple of other things to mention, but so much of what I’ve been hearing relates to the health claims that I want to address that today and let the other things spill over into next week.

When the full-spectrum term was coined in the 1960′s it referred to both visible light and the invisible ultraviolet (UV) light. The health claims of full-spectrum lighting mostly revolve around the UV end of the range. All fluorescent light emits UV radiation, since it is the UV rays created by the mercury vapor striking the phosphor coating which makes a fluorescent light work. Full-spectrum lamps just emit more UV radiation than normal lamps.

The typical recommendation is to avoid as much UV exposure as possible. UV exposure has been linked to sunburn and skin cancers as well as cataracts in the eye. UV exposure also cause the degradation of textiles, paints, and architectural materials. Museums typically require all wavelengths shorter than 400nm to be filtered out of artificial lights.

  • Technical info, you may ignore: Visible light is 760 nm to 380 nm, UVA is light wavelengths between 400 nm and 315 nm, UVB is light wavelengths between 315 nm and 280 nm, UVC is light wavelengths between 280 nm and 100 nm. Visible light is broken down as red from 760 to 610 nm, orange from 610 to 591 nm, yellow from 591 to 570 nm, green from 570 to 500 nm, blue from 500 to 450 nm, and purple from 450 to 360 nm. These are defined by the International Organization for Standardization in ISO 21348:2007.

Full-spectrum lighting to treat SAD (seasonal affective disorder): Using full-spectrum lighting does not fit into the standard treatment of SAD, which involves exposure of the eye to a white light source in a light box. The light box typically generates 10,000 lux and it is used for about 30 minutes. Lower intensities might be used for longer periods. At 10,000 lux, any light source will be effective to treat SAD. Most importantly, these light boxes shield out UV rays, which is the opposite of using full-spectrum lighting. Using full-spectrum lamps in normal overhead lighting will have no effect upon SAD treatment.

Full-spectrum lighting and vitamin D production: Vitamin D is important, but the production is stimulated by the UVB band (315 to 280 nm) of light. Full-spectrum lamps typically use phosphors to generate UVA radiation (400 to 315 nm), and they typically peak around 355 nm. You are better off eating fish and dairy products and–if you’re really worried–taking supplements. Various studies have been done showing exposure to full-spectrum lighting for vitamin D production is impractical. For example, to spike vitamin D production in your body you may need 30 hours continuous exposure to a full-spectrum lamp to get the same affect as 22 minutes of mid-day sunlight. Or, 8 hours of full-spectrum office lighting has about the same UVB exposure as 1 minute of direct sunlight.

Also, the UVB rays that are generated by full-spectrum lamps often don’t bounce off surfaces. That means that if you are hoping to increase your UVB exposure you will only get it when in direct line of sight from the lamp to your skin. Everything else is absorbed by the materials and clothing around you. That also increases the deterioration of those materials.

In summary, there really are no serious health benefits to using full-spectrum lighting.

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Full-Spectrum Lighting

Thursday, June 25th, 2009

I’ve been running into people, Tweets, and marketing articles about full-spectrum lighting recently and I want to set some things straight. Full-spectrum lighting is a marketing term used by people selling you lighting products; it does not have any technical meaning in the lighting industry. Full-spectrum sources often cost much more than a standard product, sometimes more than 10 times the cost, and the overall benefits have not been proven.

Common claims:

  • It is closer to “natural” daylight, which is its own benefit: This claim is more or less meaningless. Daylight changes throughout the day due to atmospheric conditions (is it cloudy or clear) and time of day (mid-day sun or morning sunrise). All artificial lighting sources are static in their output, what you get at 3:00 PM on a cloudy day is that same as 2:00 AM at night. Some LED sources are collections of LEDs that can be programmed to change color, but that has nothing to do with mimicking daylight. Trying to hash out the meaning of this claim gets you mired in spectral distribution curves which is a huge topic, so for now just keep in mind that “full-spectrum” sources are just modifications of existing fluorescents. Except GE Reveal and the like, which are modified incandescents.
  • You get better color from full-spectrum sources: This is sort-of true. Full-spectrum fluorescents use a different phosphor mix that can sometimes have a higher CRI (color rendering index) than a typical fluorescent. The increase in CRI is often accompanied by an decrease in efficiency. You can also get non-full-spectrum fluorescents with higher CRI ratings than standard for slightly more cost than a standard lamp but still less than a full-spectrum lamp. The stand-out exception to this is the incandescent full-spectrum sources, which decrease the CRI of their bulbs.
  • You get increased worker productivity with full-spectrum: There are two parts to this: the first is just based on the ability to see tasks well. In most circumstances productivity for visual tasks is linked to monochromatic tasks, such as reading black ink on white paper. For these tasks it is the amount of light that determines good visibility, not the color or quality of the light. In this regard full-spectrum offers no benefits. There is some research suggesting that since the rods–which are blue-green sensitive–control the size of the pupil, light to the cool, bluish side causes the pupil to constrict and thereby increase acuity and you can get equal acuity with less power by using bluish light. I think it is unreasonable to get into this kind of detail when you just want to buy a lightbulb, so the simple answer is “no.” However, if your work is very color sensitive, such as fine art or clothing production, you want to maximize the CRI of your sources to affect productivity.
  • It has psychological benefits: This is the second part of the “increased productivity” claim. By definition, a psychological benefit is “all in your head,” so in terms of the benefit claim it is true. If you like full-spectrum lighting and don’t mind the disadvantages then you are getting a psychological benefit. Does everyone feel better equally, there’s no way to say, which is why it makes a good marketing claim. I have never found any research that shows a physiological link that leads to a psychological benefit. This is also often linked to the “natural” daylight claim. It is true that most people feel better working and living under daylight than artificial light. However, daylight changes throughout the day and with the weather, and I think the change over time is one of the main reasons people like daylight.

This post is getting longer than I like for a daily reading, so I’ll deal with the health concerns tomorrow. That will give you a chance to rest up and stay with me.

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Three-Way Dimming

Tuesday, June 23rd, 2009

Yesterday, at the end of the post, I mentioned three-way and four-way dimming. For local dimmers there are two approaches: “mechanical,” and “electronic.” Mechanical and electronic refer to the dimmer type. Electronic dimmers are labeled as such and usually have LEDs on them. Mechanical dimmers are cheaper and will have no special functions and usually have a rotating dial or a slider.

For mechanical three and four way dimmers you will have to select a single location to install the dimmer, which should typically be the place from which you control the light most often. All the other locations will still be a switch that just turns the light on or off, and when turned on the lights go to the level set by the dimmer. For both three-way and four-way circuits you only use a three-way dimmer. It will have three wires instead of two (excluding the green ground wire).

Electronic dimming allows you to use remote dimmers in those locations that otherwise would have had to stay switches. However, installation is much more complex because typically there is a low-voltage wire connecting all the dimmers together. If your house doesn’t already have that wire you’re pretty much out of luck. You can use radio-controlled dimmers to eliminate the need for those extra wires, but the cost is very high (hundreds of dollars per item). Some electronic dimmer also let you use IR remote controls, and sometimes you can tie your master remote for the TV/DVD to the lights. That way you can adjust the lighting just the same as adjusting the volume on your TV. You’ll probably need to hire an electrician for those kinds of installations.

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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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