Visible Light, Additive Coloring, Subtractive Coloring, Printing and Pointilism

Posted by PITHOCRATES - August 28th, 2013

Technology 101

Our Eyes see Shades of Gray with Rods and Color with Cones

If you have colorful flower gardens all around your home and go out at night you won’t see much.  Only shades of gray.  You’ll see none of the vibrant colors of your flowers.  The moonlight, streetlights, the neighbor’s security lights, your landscaping lights, etc., will provide enough lighting so you can see your flowers.  But you won’t be able to see their colors well.  If at all.

If you go out with the bright afternoon sun shining down it’s a different story.  You can see the color.  Rich, vibrant color.  Because of the cones in your eyes.  Which can see color.  As long as it is bright enough.  Unlike the rods in your eyes.  Which work well in low light levels.  Letting you see shades of gray in low light levels.  But saturate at high light levels.  Which is where the cones take over.

Light is electromagnetic radiation.  And the key to color is the wavelength.  What is a wavelength?  Think of a guitar.  If you pluck a thick string it vibrates at one frequency.  If you pluck a thin string it vibrates at a higher frequency.  The thick string will move back and forth at a greater distance (and a slower speed) as it vibrates than the thin string.  So the thick string has a longer wavelength than the thin string.  This is a crude explanation.  But the takeaway from this is this.  As frequency decreases wavelength increases.  As frequency increases wavelength decreases.

Different Wavelengths of Light have Unique Colors and are a Small Portion of the Electromagnetic Spectrum

Light is electromagnetic radiation.  Different wavelengths of light have unique colors and are a small portion of the electromagnetic spectrum.  If you ever conducted an experiment in grade school where you passed a white light through a prism (or if you saw the cover of Pink Floyd’s Dark Side of the Moon) you saw this.  White light enters the prism and a ‘rainbow’ of colors exits the prism.  Violet on the bottom.  And red at the top.  This is the visible light spectrum.  From violet (the smallest wavelength) to blue to green to yellow to orange to red (the largest wavelength).  Wavelengths smaller than violet are ultraviolet, X-rays and gamma rays.  Wavelengths larger than red are infrared, microwave, FM, AM and long radio waves.

In low light levels rods can make out things in shades of gray.  But cannot distinguish color.  As the light intensity increases the rods saturate and lose their ability to see.  While at the same time the cones begin to see.  There are three types of rods in the eye.  Those that see long wavelengths (around the color red).  Those that see medium wavelengths (around the color green).  And those that see short wavelengths (around the color blue).  These are the primary colors of light.  Red, green and blue.  If you add any combinations of these light wavelengths together you can get any color in the visible spectrum.  The cones will ‘see’ a color based on the combination of wavelengths they sense.  If the cones sense only red and green the eye will see yellow.  If the cones sense all wavelengths equally the eye will see white.

If you’ve ever bought a color inkjet cartridge, though, you may be saying this isn’t right.  Inkjet cartridge packaging has three dots of color on them.  None of them green.  There’re red, blue and yellow.  Not red, blue and green.  Green isn’t a primary color.  Yellow is.  And that is true.  When it comes to painting.  Or printing.  Or dyeing.  That uses subtractive coloring.  Where we use dyes, inks and pigments to absorb light wavelengths.  A blue paint, for example, will absorb wavelengths of all colors but blue.  So when you look at something dyed, printed or painted blue only the blue wavelength of the source light (such as the sun) reflects onto the cones in your eye.  The other wavelengths from the source light get absorbed in the dyes, inks and pigments.  And don’t reflect onto the cones in your eyes.

Our Brain blends Wavelengths of Color together into a Continuous Color Image

Artists mix paints together on a palette.  Each individual paint absorbs a set of wavelengths.  When mixed together they absorb different wavelengths.  Allowing the artist to create a large palette of colors.  The artist applies these colors to a canvas to produce a beautiful work of art.  But not all artists.  Georges Seurat didn’t mix colors together for his masterpiece.  A Sunday on La Grande Jatte.  The subject of Stephen Sondheim’s musical Sunday in the Park with George.  Where George explains the technique he used.  Pointilism.

Instead of mixing paints together to make colors Seurat applied these paints unmixed onto the canvas.  And let the eye mix them together.  The individual pigments absorbed all wavelengths but the desired color.  As these different wavelengths of different intensities fell onto the cones the brain blended these dots of color together.  In the musical George (Mandy Patinkin in the original Broadway cast available on DVD) shows someone what the painting looks like up close.  A bunch of dots of different colors.  And then moves backward with him.  As they do the dots blend together into a rich palette of colors.  Producing a beautiful painting.

In 4-color printing we use a combination of these techniques.  Where they reproduce a color photograph by blending the three primary colors (red, blue and yellow) and black.  The original photograph is broken down into its primary colors.  Before digital printing this was done with photography and color filters.  One for each primary color.  They then made screens for each color.  To vary the intensity of each color they broke solid colors into dots.  The amount of white paper showing between the dots of ink lightened the shade of the color.  The paper runs through a press that adds each of the primary colors onto the image.  Overlapping colors to produce different colors.  Subtracting wavelengths to produce a color image.  With the brain blending these colors together to reproduce the original color photograph.  (They added black to make a cleaner image than they could by mixing the inks together to make black.)

Video displays are more like pointilism.  Televisions in the days of picture tubes had three electron guns repeatedly scanning the phosphorus coating on the inside of the picture tube.  Each gun hit one of three different colors of phosphorus.  Red, blue and green.  These dots of phosphorus glowed at different intensities.  Each pixel on the screen has one dot of each phosphorus color.  The three colors blend together into one color pixel.  We use different technology today to produce the same wavelengths of red, blue and green.  That produce a color image.  That falls on the cones in our eyes.  With our brain blending these pixels of color together into a continuous image.

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Fire, Oil Lamp, Candle, Wicks, Gas Lights, Incandescence, Incandescent Light Bulb, Fluorescence and Compact Fluorescent Lamp

Posted by PITHOCRATES - February 20th, 2013

Technology 101

(Originally published March 28th, 2012)

A Lit Match heats the Fuel Absorbed into a Wick, Vaporizes it, Mixes it with Oxygen and Ignites It

Fire changed the world.  From when Homo erectus first captured it.  Around 600,000 BC.  In China.  They saw it.  Maybe following a lightning strike.  Seeing it around volcanic activity.  Perhaps a burning natural gas vent.  Whatever.  They saw fire.  Approached it.  And learned not to fear it.  How to add fuel to it.  To transfer it to another fuel source.  To carry it.  They couldn’t create fire.  But they could manage it.  And use it.  It was warm.  And bright.  So they brought it indoors.  To light up their caves.  Scare the predators out.  To use it to heat.  And to cook.  Taking a giant leap forward for mankind.

When man moved into man-made dwellings they brought fire with them.  At first a one-room structure with a fire in the center of it.  And a hole in the roof above it.  Where everyone gathered around to eat.  Stay warm.  Sleep.  Even to make babies.  As there wasn’t a lot of modesty back then.  Not that anyone complained much.  What was a little romance next to you when you were living in a room full of smoke, soot and ash?  Fireplaces and chimneys changed all that.  Back to back fireplaces could share a chimney.  Providing more heat and light.  Less smoke and ash.  And a little privacy.  Where the family could be in one room eating, staying warm, reading, playing games and sleeping.  While the grownups could make babies in the other room.

As we advanced so did our literacy.  After a hard day’s work we went inside.  After the sun set.  To read.  Write letters.  Do some paperwork for the business.  Write an opera.  Whatever.  Even during the summer time.  When it was warm.  And we didn’t have a large fire burning in the fireplace.  But we could still see to read and write.  Thanks to candles.  And oil lamps.  One using a liquid fuel.  One using a solid fuel.  But they both operate basically the same.  The wick draws liquid (or liquefied) fuel via capillary action.  Where a porous substance placed into contact with a liquid will absorb that liquid.  Like a paper towel or a sponge.  When you place a lit match into contact with the wick it heats the fuel absorbed into the wick and vaporizes it.  Mixing it with the oxygen in the air.  And ignites it.  Creating a flame.  The candle works the same way only starting with a solid fuel.  The match melts the top of this fuel and liquefies it.  Then it works the same way as an oil lamp.  With the heat of the flame melting the solid fuel to continue the process.

Placing a Mantle over a Flame created Light through Incandescence (when a Heated Object emits Visible Light)

Two popular oils were olive oil and whale oil.  Beeswax and tallow were common solid fuels.  Candles set the standard for noting lighting intensity.  One candle flame produced one candlepower.  Or ‘candela’ as we refer to it now.   (Which equals about 13 lumens – the amount of light emitted by a source).  If you placed multiple candles into a candelabrum you could increase the lighting intensity.  Three candles gave you 3 candela of light to read or write by.  A chandelier with numerous candles suspended from the ceiling could illuminate a room.  This artificial light shortened the nights.  And increased the working day.  In the 19th century John D. Rockefeller gave the world a new fuel for their oil lamps.  Kerosene.  Refined from petroleum oil.  And saved the whales.  By providing a more plentiful fuel.  At cheaper prices.

By shortening the nights we also made our streets safer.  Some cities passed laws for people living on streets to hang a lamp or two outside.  To light up the street.  Which did indeed help make the streets brighter.  And safer.  To improve on this street lighting idea required a new fuel.  Something in a gas form.  Something that you could pump into a piping system and route to the new street lamps.  A gas kept under a slight pressure so that it would flow up the lamp post.  Where you opened the gas spigot at night.  And lit the gas.  And the lamp glowed until you turned off the gas spigot in the morning.  Another advantage of gas lighting was it didn’t need wicks.  Just a nozzle for the gas to come out of where you could light it.  So there was no need to refuel or to replace the wicks.  Thus allowing them to stay lit for long periods with minimum maintenance.  We later put a mantle over the flame.  And used the flame to heat the mantle which then glowed bright white.  A mantle is like a little bag that fits over the flame made out of a heat resistant fabric.  Infused into the fabric are things that glow white when heated.  Rare-earth metallic salts.  Which change into solid oxides when heated to incandescence (when a heated object emits visible light).

One of the first gases we used was coal-gas.  Discovered in coal mines.  And then produced outside of a coal mine from mined coal.  It worked great.  But when it burned it emitted carbon.  Like all these open flames did.  Which is a bit of a drawback for indoor use.  Filling your house up with smoke.  And soot.  Not to mention that other thing.  Filling up your house with open flames.  Which can be very dangerous indoors.  So we enclosed some of these flames.  Placing them in a glass chimney.  Or glass boxes.  As in street lighting.  Enclosing the flame completely (but with enough venting to sustain the flame) to prevent the rain form putting it out.  This glass, though, blackened from all that carbon and soot.  Adding additional maintenance.  But at least they were safer.   And less of a fire hazard.  Well, at least less of one type of fire hazard.  From the flame.  But there was another hazard.  We were piping gas everywhere.  Outside.  Into buildings.  Even into our homes.  Where it wasn’t uncommon for this gas to go boom.  Particularly dangerous were theatres.  Where they turned on the gas.  And then went to each gas nozzle with an open fire on a stick to light them.  And if they didn’t move quickly enough the theatre filled with a lot of gas.  An enclosed space filled with a lot of gas with someone walking around with an open fire on a stick.  Never a good thing.

Fluorescent Lighting is the Lighting of Choice in Commercial, Professional and Institutional Buildings

Thomas Edison fixed all of these problems.  By finding another way to produce incandescence. By running an electrical current through a filament inside a sealed bulb.  The current heated the filament to incandescence.  Creating a lot of heat.  And some visible light.  First filaments were carbon based.  Then tungsten became the filament of choice.  Because they lasted longer.  At first the bulbs contained a vacuum.  But they found later that a noble gas prevented the blackening of the bulb.  The incandescent light bulb ended the era of gas lighting.  For it was safer.  Required less maintenance.  And was much easier to operate.  All you had to do was flick a switch.  As amazing as the incandescent light bulb was it had one big drawback.  Especially when we use a lot of them indoors.  That heat.  As the filament produced far more heat than light.  Which made hot buildings hotter.  And made air conditioners work harder getting that heat out of the building.  Enter the fluorescent lamp.

If phosphor absorbs invisible short-wave ultraviolet radiation it will fluoresce.  And emit long-wave visible light.  But not through incandescence.  But by luminescence.  Instead of using heat to produce light this process uses cooler electromagnetic radiation.  Which forms the basis of the fluorescent lamp.  A gas-discharge lamp.  The most common being the 4-foot tube you see in office buildings.  This tube has an electrode at each end.  Contains a noble gas (outer shell of valence electrons are full and not chemically reactive or electrically conductive) at a low pressure.  And a little bit of mercury.  When we turn on the lamp we create an electric field between the electrodes.  As it grows in intensity it eventually pulls electrons out of their valence shell ionizing the gas into an electrically conductive plasma.  This creates an arc between the electrodes.  This charged plasma field excites the mercury.  Which produces the invisible short-wave ultraviolet radiation that the phosphor absorbs.  Causing fluorescence.

One candle produces about 13 lumens of light.  Barely enough to read and write by.  Whereas a 100W incandescent light bulb produces about 1,600 lumens.  The equivalent of 123 candles.  In other words, one incandescent lamp produces the same amount of light as a 123-candle chandelier.  Without the smoke, soot or fire hazard.  And the compact fluorescent lamp improves on this.  For a 26W compact fluorescent lamp can produce the lumen output of a 100W incandescent light bulb.  A one-to-one tradeoff on lighting output.  At a quarter of the power consumption.  And producing less heat due to creating light from fluorescence instead of incandescence.  Making fluorescent lighting the lighting of choice in commercial, professional and institutional buildings.  And any other air conditioned space with large lighting loads.

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Silicon, Semiconductor, Electrons, Holes, PN Junction, Diode, LED, Photon, 7-Segment LED and Full-Color Flat Panel LED Displays

Posted by PITHOCRATES - May 30th, 2012

Technology 101

Applying a Voltage across a PN junction to Create a Forward Bias Pushes Electrons and Holes towards the Junction

There’s gold in them thar Hills.  And silicon in the valley.  California has been a fountain of wealth.  Much of which they built from two materials located on the periodic table.  Atomic number 79.  Gold.  Or ‘Au’ as it appears on the periodic table.  And atomic number 14.  Silicon.  Or ‘Si’ as it appears on the periodic table.  Both of these metals proved to be valuable.  One by its scarcity.  One by what we could do with it.  For it was anything but scarce.  Silicon is the second most common element behind only oxygen.  But this commonly found material proved to be a greater font of wealth for California.  For it fueled the semiconductor industry.  For when we doped it with impurities we produced negatively (N-type) and positively (P-type) charged material.  Bringing the N and the P together gave us the PN junction.  Giving us the diode, transistor and integrated circuit.

The miracle of semiconductors occurs at the atomic level.  Down to the electrons orbiting the atom’s nucleus.  The nucleus contains an equal number of positively charged protons and neutrally charged neutrons.  The number of protons gives us the atomic number.  Changing the number of neutrons gives us isotopes.  Radioactive material has more protons than neutrons.  Uranium-235 is an isotope.  The stuff that made the atomic bomb dropped on Hiroshima.  Electrons orbit the nucleus.  In discrete energy levels.  The orbits closest to the nucleus have the lowest energy levels.  The orbits father away from the nucleus have higher energy levels.  Most of these orbits are ‘full’ of electrons.  The outer electron shell when ‘full’ is inert.  An outer shell that isn’t ‘full’ or has extra electrons is active.  And can chemically react.  Forming molecules.  When chemicals come into contact with each other and form molecules it is these electrons in the outer orbits (or valence electrons) that move into and out of the orbits of the different chemicals.  That is, the different elements share these valence electrons.

This is what we do when we dope silicon with impurities.  We either remove electrons from the valence shell to create a net positive charge.  Or we add electrons to the valence shell to create a net negative charge.  Giving us P-type and N-type material.  At the PN junction the N-type material loses its excess electrons to the P-type material across the junction as the empty holes in the valence shell attract the excess electrons.  As electrons leave the valence shells in the N-type material they leave holes in the valence shell where they once were.  Or, in the world of electronics, as electrons flow one way holes flow the other.  When we apply a voltage across a PN junction to create a forward bias (negative voltage applied to N-type and positive voltage applied to P-type) we push electrons and holes towards the junction.  If the forward bias is great enough they will continue all the way through the junction and into the material on the far side.  Where electrons will combine with excess holes.  And holes will combine with excess electrons.  Creating an electric current.  If we apply a voltage to create a reverse bias we will pull electrons and holes away from the PN junction.  And there will be no electrical current. We call such a PN device a diode.  A very important and indispensible device in electronics.

Placing Seven LEDs into a Figure-Eight Pattern created the Seven-Segment LED

Now back to those discrete energy levels.  There is another useful property we get when electrons move between these energy levels.  Electrons absorb energy when they move to a higher energy level.  And emit energy when they move to a lower energy level.  We make use of this property in fluorescent lighting.  A charged plasma field in a fluorescent lamp excites a small amount of mercury in the lamp.  As electrons fall into lower orbits in the mercury atoms they release invisible short-wave ultraviolet radiation.  The phosphor coating on the inside of the lamp absorbs this radiation and fluoresces.  Creating visible light.  By using different materials, though, we could see the energy (a photon) emitted by an electron falling into a lower energy level.  We have been able to move the wavelength of this photon into the visible spectrum.  The first commercial application to convert these photons into visible light was a device that gave us a red light.  That device was that important and indispensible PN-junction.  The diode.  And the use of different materials other than silicon moved these photons into the visible spectrum.  Giving us the light-emitting diode.  Or LED.

The first LEDs were only red.  Then we developed other colors using different materials.  Shifting the wavelength of the photon through all colors of the visible spectrum.  Being low-power devices, though, the intensity of light emitted was limited.  So an LED required careful mechanical construction and optics.  To direct the light out of the material forming the PN junction.  With a reflector behind the junction.  And a lens above.  To aim and diffuse the light.  And to prevent it from reflecting back into the material where it may be dissipated as heat.  Early use of LEDs was for indicator lights.  The low power consumption meant little heat was generated as with an incandescent lamp.  Which worked well in the temperature sensitive computer world.  Placing 7 LEDs into a figure-eight pattern created the seven-segment LED display.  With a rectangular shaped piece of translucent plastic above each LED you could see a bar of light for each light emitting diode.  Creating a forward bias on certain bars in the seven-segment display created the numbers we saw on our first calculators and digital watches.

An LED could produce a similar radiation like in the fluorescent lamp.  Using that radiation to fluoresce a phosphor coating inside a lamp to produce white light.  Similar to the fluorescence lamp.  Only while using less power.  Mixing the emitted light from red, green and blue (RGB) LEDs also produced white light.  Further improvements allowed us to emit whiter and brighter lights.  Allowing brighter lamps that consumed less power than the compact fluorescent lamps which were energy saving alternatives to the incandescent lamps.  With the lower power consumption of LEDs creating less heat we expanded the lifespan of lighting sources made from LEDs.  Using them to increase the service life in lamps inconvenient to change.  Like in traffic signal lights over busy intersections.  To the taillights in tractor trailers.  Where anytime spent not hauling freight was lost revenue.

We made Full-Color Flat Panel Displays from LEDs by combining Red, Green and Blue LEDs into Full-Color Pixel Clusters

The market didn’t demand these developments in semiconductors or LEDs.  For the most part the market didn’t even know this technology existed.  But the entrepreneurs gathering in Silicon Valley did.  They had some great ideas of what they could do with this new technology.  All they needed was the capital to bring these ideas to market.  It was risky.  The technology was good.  But could they use it to make useful things at affordable prices?  And would the people be so enamored with the things they built that they would buy them?  There were just too many unknowns for conservative bankers to take a risk.  But thanks to venture capitalists those entrepreneurs got the capital they needed.  Brought their ideas to market.  Created Silicon Valley.  And the modern world we now take for granted.

They continue to advance this technology.  Creating full-color flat panel displays.  By combining red, green and blue LEDs into full-color pixel clusters.  Which, unlike an LCD flat panel display, does not need a backlight as they produce their own light.  So these panels are thinner and use less power than LCD displays.  Making them ideal for the displays in our cellular devices for they allow more battery life between charges.  They also have wide viewing angles.  People looking at these displays from near perpendicular viewing angles see nearly the same quality of picture as those viewing directly in front.  Making them ideal for use in stadiums.  The video replays you see on that mammoth flat panel display in the new Dallas Cowboy stadium is an LED flat panel display.

All of this from joining two differently-charged semiconductor materials together.  Creating that all important and indispensible PN junction.  The foundation for every electronic device.  And of Silicon Valley itself.

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Fire, Oil Lamp, Candle, Wicks, Gas Lights, Incandescence, Incandescent Light Bulb, Fluorescence and Compact Fluorescent Lamp

Posted by PITHOCRATES - March 28th, 2012

Technology 101

A Lit Match heats the Fuel Absorbed into a Wick, Vaporizes it, Mixes it with Oxygen and Ignites It 

Fire changed the world.  From when Homo erectus first captured it.  Around 600,000 BC.  In China.  They saw it.  Maybe following a lightning strike.  Seeing it around volcanic activity.  Perhaps a burning natural gas vent.  Whatever.  They saw fire.  Approached it.  And learned not to fear it.  How to add fuel to it.  To transfer it to another fuel source.  To carry it.  They couldn’t create fire.  But they could manage it.  And use it.  It was warm.  And bright.  So they brought it indoors.  To light up their caves.  Scare the predators out.  To use it to heat.  And to cook.  Taking a giant leap forward for mankind.

When man moved into man-made dwellings they brought fire with them.  At first a one-room structure with a fire in the center of it.  And a hole in the roof above it.  Where everyone gathered around to eat.  Stay warm.  Sleep.  Even to make babies.  As there wasn’t a lot of modesty back then.  Not that anyone complained much.  What was a little romance next to you when you were living in a room full of smoke, soot and ash?  Fireplaces and chimneys changed all that.  Back to back fireplaces could share a chimney.  Providing more heat and light.  Less smoke and ash.  And a little privacy.  Where the family could be in one room eating, staying warm, reading, playing games and sleeping.  While the grownups could make babies in the other room.

As we advanced so did our literacy.  After a hard day’s work we went inside.  After the sun set.  To read.  Write letters.  Do some paperwork for the business.  Write an opera.  Whatever.  Even during the summer time.  When it was warm.  And we didn’t have a large fire burning in the fireplace.  But we could still see to read and write.  Thanks to candles.  And oil lamps.  One using a liquid fuel.  One using a solid fuel.  But they both operate basically the same.  The wick draws liquid (or liquefied) fuel via capillary action.  Where a porous substance placed into contact with a liquid will absorb that liquid.  Like a paper towel or a sponge.  When you place a lit match into contact with the wick it heats the fuel absorbed into the wick and vaporizes it.  Mixing it with the oxygen in the air.  And ignites it.  Creating a flame.  The candle works the same way only starting with a solid fuel.  The match melts the top of this fuel and liquefies it.  Then it works the same way as an oil lamp.  With the heat of the flame melting the solid fuel to continue the process. 

Placing a Mantle over a Flame created Light through Incandescence (when a Heated Object emits Visible Light)

Two popular oils were olive oil and whale oil.  Beeswax and tallow were common solid fuels.  Candles set the standard for noting lighting intensity.  One candle flame produced one candlepower.  Or ‘candela’ as we refer to it now.   (Which equals about 13 lumens – the amount of light emitted by a source).  If you placed multiple candles into a candelabrum you could increase the lighting intensity.  Three candles gave you 3 candela of light to read or write by.  A chandelier with numerous candles suspended from the ceiling could illuminate a room.  This artificial light shortened the nights.  And increased the working day.  In the 19th century John D. Rockefeller gave the world a new fuel for their oil lamps.  Kerosene.  Refined from petroleum oil.  And saved the whales.  By providing a more plentiful fuel.  At cheaper prices.

By shortening the nights we also made our streets safer.  Some cities passed laws for people living on streets to hang a lamp or two outside.  To light up the street.  Which did indeed help make the streets brighter.  And safer.  To improve on this street lighting idea required a new fuel.  Something in a gas form.  Something that you could pump into a piping system and route to the new street lamps.  A gas kept under a slight pressure so that it would flow up the lamp post.  Where you opened the gas spigot at night.  And lit the gas.  And the lamp glowed until you turned off the gas spigot in the morning.  Another advantage of gas lighting was it didn’t need wicks.  Just a nozzle for the gas to come out of where you could light it.  So there was no need to refuel or to replace the wicks.  Thus allowing them to stay lit for long periods with minimum maintenance.  We later put a mantle over the flame.  And used the flame to heat the mantle which then glowed bright white.  A mantle is like a little bag that fits over the flame made out of a heat resistant fabric.  Infused into the fabric are things that glow white when heated.  Rare-earth metallic salts.  Which change into solid oxides when heated to incandescence (when a heated object emits visible light).

One of the first gases we used was coal-gas.  Discovered in coal mines.  And then produced outside of a coal mine from mined coal.  It worked great.  But when it burned it emitted carbon.  Like all these open flames did.  Which is a bit of a drawback for indoor use.  Filling your house up with smoke.  And soot.  Not to mention that other thing.  Filling up your house with open flames.  Which can be very dangerous indoors.  So we enclosed some of these flames.  Placing them in a glass chimney.  Or glass boxes.  As in street lighting.  Enclosing the flame completely (but with enough venting to sustain the flame) to prevent the rain form putting it out.  This glass, though, blackened from all that carbon and soot.  Adding additional maintenance.  But at least they were safer.   And less of a fire hazard.  Well, at least less of one type of fire hazard.  From the flame.  But there was another hazard.  We were piping gas everywhere.  Outside.  Into buildings.  Even into our homes.  Where it wasn’t uncommon for this gas to go boom.  Particularly dangerous were theatres.  Where they turned on the gas.  And then went to each gas nozzle with an open fire on a stick to light them.  And if they didn’t move quickly enough the theatre filled with a lot of gas.  An enclosed space filled with a lot of gas with someone walking around with an open fire on a stick.  Never a good thing.

Fluorescent Lighting is the Lighting of Choice in Commercial, Professional and Institutional Buildings 

Thomas Edison fixed all of these problems.  By finding another way to produce incandescence. By running an electrical current through a filament inside a sealed bulb.  The current heated the filament to incandescence.  Creating a lot of heat.  And some visible light.  First filaments were carbon based.  Then tungsten became the filament of choice.  Because they lasted longer.  At first the bulbs contained a vacuum.  But they found later that a noble gas prevented the blackening of the bulb.  The incandescent light bulb ended the era of gas lighting.  For it was safer.  Required less maintenance.  And was much easier to operate.  All you had to do was flick a switch.  As amazing as the incandescent light bulb was it had one big drawback.  Especially when we use a lot of them indoors.  That heat.  As the filament produced far more heat than light.  Which made hot buildings hotter.  And made air conditioners work harder getting that heat out of the building.  Enter the fluorescent lamp.

If phosphor absorbs invisible short-wave ultraviolet radiation it will fluoresce.  And emit long-wave visible light.  But not through incandescence.  But by luminescence.  Instead of using heat to produce light this process uses cooler electromagnetic radiation.  Which forms the basis of the fluorescent lamp.  A gas-discharge lamp.  The most common being the 4-foot tube you see in office buildings.  This tube has an electrode at each end.  Contains a noble gas (outer shell of valence electrons are full and not chemically reactive or electrically conductive) at a low pressure.  And a little bit of mercury.  When we turn on the lamp we create an electric field between the electrodes.  As it grows in intensity it eventually pulls electrons out of their valence shell ionizing the gas into an electrically conductive plasma.  This creates an arc between the electrodes.  This charged plasma field excites the mercury.  Which produces the invisible short-wave ultraviolet radiation that the phosphor absorbs.  Causing fluorescence.

One candle produces about 13 lumens of light.  Barely enough to read and write by.  Whereas a 100W incandescent light bulb produces about 1,600 lumens.  The equivalent of 123 candles.  In other words, one incandescent lamp produces the same amount of light as a 123-candle chandelier.  Without the smoke, soot or fire hazard.  And the compact fluorescent lamp improves on this.  For a 26W compact fluorescent lamp can produce the lumen output of a 100W incandescent light bulb.  A one-to-one tradeoff on lighting output.  At a quarter of the power consumption.  And producing less heat due to creating light from fluorescence instead of incandescence.  Making fluorescent lighting the lighting of choice in commercial, professional and institutional buildings.  And any other air conditioned space with large lighting loads. 

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