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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Light, Particles, Waves, Polarization, Liquid Crystal, Twisted Nematic Effect, LCD, CRT, Pixel and Thin-Film Transistors

Posted by PITHOCRATES - June 13th, 2012

Technology 101

Light is Electromagnetic Radiation consisting of a Vertical Electric Wave and a Horizontal Magnetic Wave

The sun lights our day.  And artificial sources of light do the same for our nights.  We see light.  Light rays behave both like a wave.  And like particles.  Complicated stuff.  And fascinating.  The kind of stuff that physicists pass their day thinking about.  But we’re not going to delve into that complicated stuff.  Just the waves. 

Light is electromagnetic radiation.   A light wave has an electric portion.  And a magnetic portion.  Or an electric field.  And a magnetic field.  In other words a light ray is made up of two waves.  Think of the up-and-down sinusoidal wave you see on an oscilloscope.  When you look at the scope this waveform moves from left to right.  It rises up on an angle.  Then bends and curves down at the peak amplitude of the wave until it is moving down at an angle.  Then it bends and curves up at the bottom of the wave and rises up again on an angle.  Again and again.  Now imagine this waveform existing in the open air just as it appears on the scope.  Turn the wave 90 degrees so it is moving towards you.  Going up and down.  Now imagine a second wave doing the exact same thing.  Coming towards you going up and down.  Now rotate that second wave 90 degrees so it’s going side-to-side as it approaches you.  Now you have one wave coming at you going up-and-down.  And a second wave coming at you going side-to-side.  This is a light wave.  The up-and-down wave is the electric field.  And the side-to-side wave is the magnetic field. 

Because of these properties we can do things with light.  For example, if you’re driving into the sun there will be a blinding glare coming off of the road.  It’s annoying.  And rather dangerous.  This glare is a reflected light wave.  And it so happens that these reflected waves are also magnetic waves.  The side-to-side waves.  Which brings us to something interesting we can do about this glare.

When you Apply an Electric Field to a Liquid Crystal the Molecules Orientate themselves as they would be in a Crystal

A polarized lens is a light filter.  It will only pass light that is oriented in the same polarization.  Think of a picket fence.  Built from vertical slats of wood (or pickets) with some open space in between.  Imagine bouncing a ball like a sinusoidal wave directed at the open spaces between the pickets.  The ball will pass through.  Now rotate a part of that fence 90 degrees.  So the pickets run horizontally.  And bounce the ball towards the fence.  As the ball descends on an angle towards one of the vertical spaces it may clear the top edge of one picket but will bounce off of the top edge of the next picket down.  When the spaces of the pickets are oriented 90 degrees out of phase with the plane of the bouncing ball it block the ball from passing through.

This is how a polarized lens works.  It only passes light waves that are in phase with the lens.  And blocks the waves that are out of phase with the lens.  Which is a very handy property to have when you’re driving into the sun.  Because you can wear polarized sunglasses that pass only the up-and-down waves.  And block the side-to-side waves.  If you have two pairs of polarized sunglasses you can experiment like a physicist.  Hold up both pairs in the same orientation.  Like wearing two pairs of sunglasses.  You’ll be able to see through them.  Glare-free.  Now if you slowly rotate one lens 90 degrees you’ll see the lenses turning opaque.  Blocking more and more light until they block all light.  Both the up-and-down waves.  And the side-to-side waves.

This experiment in physics was interesting.  But it’s what we can do with this knowledge that is fascinating.  When we combine it with an interesting material.  That has the properties of a liquid.  And a crystal.  We call this material a liquid crystal (LC).    If we carefully select the type of liquid crystal material and carefully apply a voltage we can make this LC do what we did by rotating one polarized lens in front of another.  And the big breakthrough that made liquid crystal displays (LCD) possible was the twisted nematic effect (TN-effect).

In Color Displays a Cluster of Three LCDs (Red, Green and Blue) form a Pixel

An LCD is made in layers.  The first layer you look through is a polarizing filter with a vertical axis.  This lets only the up-and-down waves through.  The second layer is a glass with a conducting oxide substrate forming electrodes.  These form one side of the electrodes that set up an electric field.  This is a thin film that is both electrically conductive and transparent.  In a clock or a calculator we could apply this in the layout of sequential 7-segment displays.  Where to display a number we apply a voltage to the appropriate segments.  The third layer is the twisted nematic liquid crystal.  The fourth layer is a glass with another transparent conducting oxide substrate film. This is the other side of the electrodes that set up the electric field.  But this is a common electrode without any patterns in it.  The fifth layer is another polarizing lens.  Only this one has a horizontal axis to pass only the side-to-side waves.  The sixth layer is either a reflective surface to bounce back the light that reaches it.  Or it’s a light source to send light from the back out through the front of the LCD display.

The key for making the LCD work is the TN-effect.  In the un-energized state the crystals form a helical structure.  Like the twisting pairs of DNA.  This helix twists 90 degrees.  When light enters it this crystal structure rotates the light waves 90 degrees.  Allowing this light wave to pass through the second polarized lens.  And reflect back out.  Imagine a calculator with an LCD display switched off (or without any batteries).  All you will see is a blank display.  When the electrodes are energized, though, the crystals untwist and align in phase with the light entering it.  So the light passes through the crystal without rotating.  And is blocked by the second polarized lens.  By energizing the appropriate segments of the 7-segment display the light waves the LC blocks form the numbers we see.  By varying the voltage across the electrodes you get the same effect we saw when we rotated one pair of polarized sunglasses behind another pair.  We block varying amounts of light through the crystal.  Which modulates the intensity of the passed-through light.

LCDs work with small voltages.  Better yet, they need no current other than the backlight and the electronics that drive them.  Making them ideal for battery-powered devices.  Like lap-top computers.  Tablets.  Smartphones.  And even for things that plug into electrical outlets.  Like televisions.  Which produce very little heat unlike the cathode ray tubes (CRT) they replaced.  In color displays they use the same principle.  Only a cluster of three LCDs (red, blue and green) form a pixel.  We place a color filter in front of the LCD to pass only that color’s wavelength of light.  And each pixel has a thin-film transistor (TFT) added to that transparent conducting oxide substrate film (in an active display matrix).  A TFT varies the amount of light passed through an LCD.  Combinations of intensity of each pixel create all the different colors.  And the different colors of the pixels produce the images we see.

LCD technology has come a long way thanks to a lot of profit-seeking people.  For imagine what would happen if the CRT manufacturers had successfully lobbied government to protect their industry by hurting the LCD industry.  It’s happened throughout time.  Rent-seekers who tried to buck change and innovation.  So they could still profit on last year’s technology.  By blocking new technology from reaching the people.  Forcing them instead to pay higher prices for their inferior products.  Thankfully the profit-seekers dominate the LCD market.  Which is why we have laptops, tablets and smartphones.  And will soon no doubt have even better devices.  Because these profit-seekers are always working on something newer.  And better.  While the rent-seekers hang onto the past.  Frozen in time.  Using the power of government to protect jobs that build products the people would rather not buy.  Causing economic stagnation.  And a lower standard of living.

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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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