Artificial lighting

[Joan Breckwoldt]

Hi Mike,

Thank you for your reply. I have a bulb that looks like that but made my Commercial Electric, I got it at Home Depot. It's a flourescent. Do you know what Kelvin rating yours has?

Joan

[Joan Breckwoldt]

I just checked that website, say's that bulb is rated at 5500 Kelvin. Hmm, I think mine might be higher.

Okay, here's a question. Does all flourescent light put out the same temperature light? It seems like it would.

Joan

[Michael Georges]

Originally Posted by Joan Breckwoldt

I just checked that website, say's that bulb is rated at 5500 Kelvin. Hmm, I think mine might be higher.

Okay, here's a question. Does all flourescent light put out the same temperature light? It seems like it would.

Joan

I don't believe so. Your standard commercial flourescent bulb is between 3000 and 4000 K with a CRI somewhere between 50 and 80. They are much more yellow-shifted.

[Joan Breckwoldt]

Well Michael, that explains a lot, if what I got from Home Depot falls under 'standard commercial bulb'. But, how can it be that one flourescent bulb puts out 5500K and another 3000K? I don't understand that.

Joan

[Joan Breckwoldt]

I found a website that gave me some information on flourescent lamps. I have copied some of the info below:

Fluorescent Phosphors The color of fluorescent lamps is created by mineral phosphors in powder form which coat the inside of the lamp tube. The chemical make-up of these phosphors determines the lamps CRI, its Color Temperature, and how much light the lamp produces. There are four types of phosphor coatings:

Traditional halophosphors Are inexpensive coatings which usually provide the entire spectrum of light. But, there is a trade-off between Color Rendering and Lumen output. Poor color rendering lamps such as "warm white" and "cool white" have high Lumen output. Good color rendering lamps such as "warm white deluxe" and "cool white deluxe" have low Lumen output.

Prime color or Tri-phosphors Are very expensive coatings with good color rendering and high lumen output. Lamps of this type are produced under the trademark, Ultralume.

Double-coat lamps Have a coat of halo-phosphor and a coat of tri-phosphor. Double-coat lamps which have a thick tri-phosphor coat are fairly expensive but have very good color rendering properties. They are known by the trademarks SPX, Designer 800 series, etc.. Double-coat lamps with a thin tri-phosphor coat are much less expensive, but still have full light output and reasonably good color rendering. These lamps are known by the trademarks SP, SPEC, Designer, and others.

Rare Earth Phosphors Have a thin and thick coat of rare earth phosphors and are just becoming available. The CRI for these lamps will be 70, 80, and 90 and in a variety of Color Temperatures.

Whew, that's more than I wanted to know but at least it convinces me that all "flourescent" lamps are not equal.

The bulb I'm using doesn't have any info about it's temperature and their website had a range, just like you said Michael. So, I guess the best way is experimentation and maybe try that Verilux bulb.

Joan

P.S. This is where I found the above info:http://www.lightcalc.com/glossary.html

[Joan Breckwoldt]

The Commercial Electric (that's the brand name) website says this about it's screw-in bulbs: "This fluorescent 42 watt has one of the highest light outputs available. It comes in two colors, 2700k and 5100k full spectrum daylight. They screw in to almost any socket and put out the same amount of light as a 150 watt light bulb." But, unbelievably, there is no info on the package of my bulb indicating which bulb I have. My package says "warm white light" and that it's equivalent to 75 Watts light output. This light was meant to go in a table light to help someone read better so I guess this info isn't important to the general public. Time to buy a bulb that I know something about so at least I can begin to understand why a photo I take is too warm, cool, etc.

Joan

[Dan Landrie]

Hi I'm an electrician, ballast are actually rated by how much noise they make the rating method is alphabetical with a sound rating of "A"being the quietest it will say on the ballast label what the sound rating is.

[ReNae Stueve]

You will find if you really learn as much as you can about the fluorescent world that there is a catch 22 here. Be an informed consumer.

Self ballasted compacts or CFL lamps that you screw into your table lamps are typically designed for residential use and as such are an FCC class B EMI ballast EMI protects againt electromagnetic and radio frequesncy interference. (so you don't have to wear tin foil on your head. ) they are electronic an as such do not have a noise factor that the old electromagnetics had. Temp is usually 27K although almost never rated. CRI is not a goal or constant through the life of the lamp. These lamps are designed to save energy not provide critical task light.

This is the case with all fluorescent lighting systems. I use the word "systems" because the product is always a ballast and lamp working together to produce a desired effect. And that goal is by design, long life and lower watts per lumen. CRI and other ratings are used only to compare them to their like product family members.

Even though many aftermarket labelers are promoting home CFL's as some kind of magic light, these claims are not in any way true. Please be informed as a consumer, What you pay $100.00 plus for is sold by Graybar and GE for $5.85, and all are made by 4 companies in the US and China and are relabeled for residential and home depot sales. ata very high profit

[ReNae Stueve]

the following is takend from GE's lighting specification index.

I hope it helps

Warm," Cool," Daylight," etc.


Yellowish white light, reminding people of a fireplace, is called "warm" while bluish white light is called "cool." These are based on associations with these colors. "Daylight" is supposed to mimic light coming in from a window. These are crude, but useful classifications. However, we can have differing degrees of "cool" and "warm": and therefore we need a quantitative measure, the Correlated Color Temperature, described below.

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Correlated Color Temperature (CCT) measured in Kelvins (K)

Figure 3
Correlated Color Temperature (measured in Kelvins)-or simply Color Temperature-is a scientific scale to describe how "warm" or how "cool" the light source is. It is based on the color of light emitted by an incandescent source. As a piece of metal (a theoretical Blackbody) is heated, it changes color from reddish to orange to yellowish to white to bluish-white. The color of light emitted by an incandescent object depends only on the temperature. We can use this scale to describe the color of a light source by its "Color Temperature."

When we say a lamp has a Color Temperature of 3000 Kelvins, it means a glowing metal at 3000 Kelvins would produce light of about the same color as the lamp. Instead, if the metal is heated to 4100 Kelvins, it will produce a much whiter light. Direct sunlight corresponds to about 5300 Kelvins while daylight, which has the blue from the sky mixed in, is typically 6000 Kelvins or above. A standard incandescent lamp has a filament at 2700 Kelvins, and therefore (by definition) a Color Temperature of 2700 Kelvins.

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Color Rendering Index (CRI)

Figure 4
Color Rendering Index (maximum =100) is a measure of how closely the lamp renders colors of objects compared to a standard source. Implied is that the standard source is ideal, which may not always be true. Daylight is considered a standard but then so also is any "Blackbody," i.e. any incandescent object, no matter what its temperature. Based on this definition, daylight and all incandescent and halogen sources have CRI's of 100. For a warm lamp, CRI is a measure of how close to incandescent color it is; for a very cool lamp it is how close to daylight it is. Sources with very distorted colors will have low CRI. In general, the higher the CRI the more natural the appearance of the source and the richer colors appear. More information on CRI is provided in another section.
Color Rendering

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C.I.E. Chromaticity Diagram


The C.I.E. (Commission Internationale de l'Eclairage, the International Commission on Color) diagram is based on the idea that mixing varying proportions of three hypothetical primaries (not necessarily red green and blue) can create the sensation in the human observer, of any color of light. The three "primary" colors are dubbed "X," "Y," and "Z." If we are merely concerned about color and not about brightness, we can specify just the relative strengths of these three colors, denoted by x, y and z. Since x + y + z must add up to 1 (i.e. 100%) just providing x and y is sufficient to specify lamp color; the z value is implied. Lamp color can then be represented on a two-dimensional plot of x and y. All possible colors then fall under a "guitar-pick" shaped triangle in which the perimeter encompasses spectrally pure colors (seen in nature only in rainbows and prisms) ranging from red to blue. Moving toward the center "dilutes" the color until it ultimately becomes "white". Specifying the x,y coordinates locates a color on the color triangle.

The color points traversed by an incandescent object as its temperature is raised can be plotted on the CIE Chromaticity diagram as the "Blackbody curve" and occupies the central white region. Two lamps whose x,y co-ordinates fall one above the Blackbody curve and one below could have the same CCT. However, the one above will appear slightly greener, and the one below slightly pinker. This is why two lamps having the same color temperature can still show differences in color as seen by the human eye. Color is complex; attempting to describe the lamp color with just one number (or even with two numbers) does not provide total information on how different materials will appear under that light.

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Spectral Power Distribution (SPD) Curves


The most complete description of lamp color characteristics can only be provided by a detailed plot of relative power emitted in the different regions of the spectrum. Such a plot with color shadings to indicate the colors corresponding to the different wavelengths is very useful in providing a visual feel for the color balance in a lamp. Such spectral curves for a number of lamps are provided in another section. See Spectral Power Distribution Curves.