Kelvin in Lighting

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Dnkldorf

Senior Member
How can the same bulb come in 2700K, 3500K, 4700K?



Is there a different gas pressure, or gas mixture that increases or decreases this?
 

cpal

Senior Member
Location
MA
I would also be intersted in an informed answer, I always thought that the Temp in K indicated the color of the light. the higher the temp the closer to white. but I may be getting that confused with CRI. Try Chp 9 in American Electricans HB. Mines packed away.
 

hurk27

Senior Member
How can the same bulb come in 2700K, 3500K, 4700K?



Is there a different gas pressure, or gas mixture that increases or decreases this?
No just different elements in the gas mixture,

I would also be interested in an informed answer, I always thought that the Temp in K indicated the color of the light. the higher the temp the closer to white. but I may be getting that confused with CRI. Try Chp 9 in American Electricians HB. Mines packed away.
you are correct, the K rating system is the same system they use in photography, the higher the K the closer to the natural light of the sun.

2700 to 3200 = normal incandescent lamps
3800 to 4500 = halogen lamps
4600 to 6500 = is starting to get close to the color of the sun light, but will look blueish, if you have other lower color temp lamps in the area.
 

shamsdebout

Senior Member
Location
Macon,GA
How can the same bulb come in 2700K, 3500K, 4700K?



Is there a different gas pressure, or gas mixture that increases or decreases this?

For Incandescence the physical make up of the filament to produce a certain temperature.
For Photoluminescence you can vary the spectral distribution by the chemical makeup of the gas to produce higher or lower correlated color temperature.

I guess technically if you induce a higher voltage and higher current and of course not use a ballast to regulate the current in the arc the lamp would get hot and you never know what color correlated temperature you will get then.
 

SG-1

Senior Member
So the gas mixture is different then....

Would it be possible to use one set gas mixture, and change the color via voltage input?
I think hurk27 is refering to the metal filament having a different composition.

Increased or decreased voltage can change the colour temperature. Especially notable on incandecents.

So far as the colour temperature of sunlight is concerned it does not have one exact temperature. If you had a meter that could measure it you would find the temperature varies depending on the time of day. The most eye pleasing temperatures occur when the shadows are long in the morning or the evening. The colour is creamier then. The atmosphere causes this temperature shift. Many photographers only shoot during those times.

Another way to change the colour temperature of a light source is a coloured filter.
 

badabing

Member
I have a question that may go with this topic. We order a lot of T8 bulbs at work. We spec 3500k, but order from different suppliers. Each supplier it seems has a different take on what a 3500k bulb's 'color' should be. Isn't there some kind of standard? We order from GE, Sylvania, Damark, TCP, etc... and some are pinkish, others brighter, and some greener. None are the same color, but all state they are 3500k. We're attempting to change all of our bulbs to the TCP color which seems to be the best, but it's difficult to have to order from just one mfg. So i guess my question is, is there a standard for the colors that should be emitted from the bulb at it's kelvin temp, or is it left up to the mfg to decide?
 

gar

Senior Member
090925-1923 EST

Flouresecent lamps have a color that is determined by the phosphors that coat the inside of the tube. The gas in the tube is used to excite the phosphor coating. The excitation is probably all from the ultra-violet region and the reason mercury is in these bulbs.

See some of these sites:

www.home.howstuffworks.com/question236.htm

http://home.howstuffworks.com/fluorescent-lamp.htm/printable

Spectral curves:

This GE site is excellent. Only two curves at a time can be compared.
http://www.gelighting.com/na/business_lighting/education_resources/learn_about_light/distribution_curves.htm

http://www.pets-warehouse.com/Aqualitchart.html

Useful information:

http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/troffer_benchmark_01-09.pdf

.
 

gar

Senior Member
090925-2055 EST

An incandescent source, light bulb or molten iron,etc., have an approximately continuous spectrum of output colors (frequencies). A idea black body radiator can be described by an equation. The hotter it is the shorter is the wavelength of peak radiation. The peak radiation is its color temperature and the temperature of the black body. See
http://en.wikipedia.org/wiki/Black_body

Generation of colors from phosphors are of somewhat narrow band outputs. The composition of the various phosphors in a lamp will determine how your eye responds with its three primary color detectors.

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Dnkldorf

Senior Member
Is the phosphur colored somehow for the desired output?

I take it, it couldn't be applied as a clear coating.
 

gndrod

Senior Member
Location
Ca and Wa
How can the same bulb come in 2700K, 3500K, 4700K?



Is there a different gas pressure, or gas mixture that increases or decreases this?
In fluorescent lamps, the inner tube wall is coated with a mix of rare earth phosphors that when excited from electron interaction will vibrate and glow at a varied frequency in a different visible hue.

In LED's, the chip element when energized emits a different frequency that varies in Kelvin temperatures desired for mood (2000-3500K) or task (4500-6700K)+ lighting ranges.
The chip element can also be doped to change the color hue output.

This is as untechnical as an explanation I can give without putting anyone in a deep sleep. rbj
 

gar

Senior Member
09026-0824 EST

From
http://electronics.howstuffworks.com/tv6.htm
How Television Works
by Marshall Brain

Print Cite Feedback E-mail This Facebook Digg This Yahoo! Buzz StumbleUpon TwitThis Reddit Share Recommend Cite This!Close
Please copy/paste the following text to properly cite this HowStuffWorks article:


Brain, Marshall. "How Television Works." 26 November 2006. HowStuffWorks.com. <http://electronics.howstuffworks.com/tv.htm> 26 September 2009.
Inside this Article
Introduction to How Television Works
TV Pixels and Your Brain
TV Motion and Your Brain
The Cathode Ray Tube
Inside a CRT
TV Steering Coils
See more ?
TV Phosphors
The Black-and-White TV Signal
Painting the TV Screen
Composite Video Signal
Color TV Screen
Color TV Signal
TV Broadcasts
VCR and Cable Signals
Satellite TV Signals
Digital TV
Monitors vs. TVs
More Information on TV
See all TV Technology articles
Electronics Videos

More Electronics Videos ?

TV Phosphors
A phosphor is any material that, when exposed to radiation, emits visible light. The radiation might be ultraviolet light or a beam of electrons. Any fluorescent color is really a phosphor -- fluorescent colors absorb invisible ultraviolet light and emit visible light at a characteristic color.
In a CRT, phosphor coats the inside of the screen. When the electron beam strikes the phosphor, it makes the screen glow. In a black-and-white screen, there is one phosphor that glows white when struck. In a color screen, there are three phosphors arranged as dots or stripes that emit red, green and blue light. There are also three electron beams to illuminate the three different colors together.

There are thousands of different phosphors that have been formulated. They are characterized by their emission color and the length of time emission lasts after they are excited.
Then go to
http://science.howstuffworks.com/light4.htm
Producing a Photon
Any light that you see is made up of a collection of one or more photons propagating through space as electromagnetic waves. In total darkness, our eyes are actually able to sense single photons, but generally what we see in our daily lives comes to us in the form of zillions of photons produced by light sources and reflected off objects. If you look around you right now, there is probably a light source in the room producing photons, and objects in the room that reflect those photons. Your eyes absorb some of the photons flowing through the room, and that is how you see.
There are many different ways to produce photons, but all of them use the same mechanism inside an atom to do it. This mechanism involves the energizing of electrons orbiting each atom's nucleus. How Nuclear Radiation Works describes protons, neutrons and electrons in some detail. For example, hydrogen atoms have one electron orbiting the nucleus. Helium atoms have two electrons orbiting the nucleus. Aluminum atoms have 13 electrons orbiting the nucleus. Each atom has a preferred number of electrons orbiting its nucleus.

Electrons circle the nucleus in fixed orbits -- a simplified way to think about it is to imagine how satellites orbit the Earth. There's a huge amount of theory around electron orbitals, but to understand light there is just one key fact to understand: An electron has a natural orbit that it occupies, but if you energize an atom you can move its electrons to higher orbitals. A photon of light is produced whenever an electron in a higher-than-normal orbit falls back to its normal orbit. During the fall from high-energy to normal-energy, the electron emits a photon -- a packet of energy -- with very specific characteristics. The photon has a frequency, or color, that exactly matches the distance the electron falls.

There are cases where you can see this phenomenon quite clearly. For example, in lots of factories and parking lots you see sodium vapor lights. You can tell a sodium vapor light because it is very yellow when you look at it. A sodium vapor light energizes sodium atoms to generate photons. A sodium atom has 11 electrons, and because of the way they are stacked in orbitals one of those electrons is most likely to accept and emit energy (this electron is called the 3s electron, and is explained on this page). The energy packets that this electron is most likely to emit fall right around a wavelength of 590 nanometers. This wavelength corresponds to yellow light. If you run sodium light through a prism, you do not see a rainbow -- you see a pair of yellow lines.
There are mixtures of different phosphors coating the inside of the fluorescent tube. The structure of particular phosphors and the combination of different phosphors and their concentration determines the bulb's color.

Do your own library or Google search for much more information on this subject.

.
.
 

tjbaudio

Member
So the gas mixture is different then....

Would it be possible to use one set gas mixture, and change the color via voltage input?
This is from a theater back ground.
The filament is different in physical dimension. There are several factors we look at:

light output in Lumens
rated voltage
color temp
rated life

All of these are related to thickness and length of the filament wire and how it is coiled. A higher color temp usually means a lower rated life. Long life lamps have a lower color temp and lower output. It is all a trade off. How small the filament can be wound also impacts the efficiency of the optics in lighting instruments. We are seeing double wound filaments. ETC has there Source4 lighting units. The S4 lamp (ansi code HPLXXX) has 4 small filaments in close proximity.

We can use color correcting filters to match color temp as well. However your throwing away light output. Another concept we have to deal with is amber shift. As you dim an incandescent lamp its color temp drops, the output gets more amber. It is even more of a problem now that many of the lights are HMI or other discharge type lamp. Those type use mechanical dimming. LEDs are also getting very popular on stage and those also do not have any amber shift.
 

Mr. Bill

Senior Member
Location
Michigan
How can the same bulb come in 2700K, 3500K, 4700K?

Is there a different gas pressure, or gas mixture that increases or decreases this?
Different mixtures of phosphor coatings make the different colors. Fluorescent lamps make ultraviolet light. The phosphor changes the wavelength of this light to our visible spectrum. Most fluorescent have a mixture of 3 different phosphors to make a broader range of visible light.
I always thought that the Temp in K indicated the color of the light. the higher the temp the closer to white.
Temp in Kelvin does not measure "whiteness" of light. I heard of one firm in Las Vegas that has a wall of 20-30 white lights. When a client tells them they want white light they walk them over to the wall and tell them to pick which one they think is white. The higher Kelvin lamps are often marketed and sold as full spectrum, or similar to natural sunlight. This is just marketing BS to get your money.

3000K is a bit redish
4100K is a bit bluish
6500K is very bluish. Does not pick up the reds in peoples faces and can make people appear ghostly.
in the late 1800s, the British physicist William Kelvin heated a block of carbon. It glowed in the heat, producing a range of different colors at different temperatures. The black cube first produced a dim red light, increasing to a brighter yellow as the temperature went up, and eventually produced a bright blue-white glow at the highest temperatures. In his honor, Color Temperatures are measured in degrees Kelvin.
The system for measuring light is not perfect but it's what we have to work with. Measuring the color of white light is odd when referencing this old experiment. I don't know of any better system.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
The phosphor changes the wavelength of this light to our visible spectrum.
Actually, the phosphors don't "change the wavelength" of the UV, they fluoresce from being bombarded by the UV. All of the visible light comes from the coating glowing.
 

Mr. Bill

Senior Member
Location
Michigan
Actually, the phosphors don't "change the wavelength" of the UV, they fluoresce from being bombarded by the UV. All of the visible light comes from the coating glowing.
Sure it does.
This energy causes the phosphor coating on the inside of the tube to ?fluoresce,? converting the ultraviolet into visible light.
http://www.sylvania.com/Lighting101/LearnLighting/LightAndColor/FluorescentTechnology/
Ultraviolet light into the phosphor, Visible light out of the phosphor. I don't know what else to call it other than the phosphor is changing the light's wavelength.
This is where the tube's phosphor powder coating comes in. Phosphors are substances that give off light when they are exposed to light. When a photon hits a phosphor atom, one of the phosphor's electrons jumps to a higher energy level and the atom heats up. When the electron falls back to its normal level, it releases energy in the form of another photon. This photon has less energy than the original photon, because some energy was lost as heat. In a fluorescent lamp, the emitted light is in the visible spectrum -- the phosphor gives off white light we can see. Manufacturers can vary the color of the light by using different combinations of phosphors.
http://home.howstuffworks.com/fluorescent-lamp.htm/printable
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
They may be said to convert the energy, but it's not a simple color-change by filtering the light. These are new photons, not the UV photons vibrating at a new frequency.
 
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