Let there be light
An short introduction to the history and future of lighting
More to follow in PART 2 History of lighting – I
Evidence of lighting goes back to 70,000 BC
Hollow rocks or shells or other natural found objects were filled with moss or a similar material that was soaked in animal fat and then ignited History of lighting - II 4,500 BC Early pottery lamps appear – simple wicks and animal oils History of lighting - III
3,000 BC Invention of candles. Still in use as the prime source of light up to the 17th century History of lighting - IV
900 AD A Persian polymath - Muhammad ibn Zakariya Raz invents the kerosene lamp
Amongst many other things he distilled petroleum and was considered the father of paediatrics and opthalmology. History of lighting - V 1780 AD Aimé Argand, a Swiss physicist and chemist greatly improved oil lamp efficiency and performance with improved oils and the use of glass chimneys to draft the flame. History of lighting - VI 1792 William Murdoch began experimenting with gas lighting and probably produced the first gas light in this year History of lighting - VII
1881 First gas mantle (Welsbach) 60% magnesium oxide; 20% lanthanum oxide; 20% yttrium oxide
1891 Successful gas mantle. 99% thorium dioxide; 1% cerium dioxide. Problems with radioactive decay products History of lighting -VIII
1841 Welcome to the electric lamp! An arc light demonstration in Paris History of lighting -VIII
1876 Pavel Yablochkov invented the Yablochkov candle, the first practical carbon arc lamp History of lighting
To be continued another day Lighting can be confusing
Tungsten halogen
Many different shapes and sizes Lighting can be confusing
Compact Fluorescent Lamp
Many different types of discharge lamp New LED technology
60 individual LED units in a GU10 shape
Example of individual LED units in a conventional 60 mm bulb shape Time to get rid of the fog! What is light?
A simple definition of light is visually perceived radiant energy
This visible light is a tiny part of the electromagnetic spectrum and ranges in wavelengths from 380 nm to 780 nm The Electromagnetic Spectrum
Wavelength in metres Energy and frequency
Wavelength is inversely proportional to frequency. A wavelength of 1 metre corresponds to a frequency of 300 MHz.
Yellow light from a low pressure sodium lamp with a wavelength of 588.995 has a frequency of 5.09 * 1014 Hz
The energy contained in one packet of light is proportional to frequency
So shorter wavelength energy contains more energy.
That is why UV light is damaging and X rays are even more damaging 6,000,000 candlepower floodlight in wartime
But what is candlepower?
Time for a few definitions Some old definitions - I
Candlepower is an obsolete unit expressing luminous intensity, equal to 0.981 candelas. It expresses levels of light intensity in terms of the light emitted by a candle of specific size and constituents. In modern usage candlepower equates directly to the unit known as the candela Some old definitions - II
Foot candle is a unit of illumination (now little used) equal to that given by a source of one candela at a distance of one foot What is the Candela?
Candela The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1⁄683 watt per steradian It needs to be much simpler!
Lumen The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total quantity of visible light emitted by a source.
Lux LUX is the measurement of actual light available at a given distance. A lux equals one lumen incident per square metre of illuminated surface area. The European Energy Label Two sides to the label
Still looks complicated but is simple to decode
The left hand side gives an immediate idea of energy efficiency
The right hand side gives all the details The left hand side
The left hand side of this label gives an immediate idea of energy efficiency.
In this case the information is both graphical and text based. Strive for an A++ rating The right hand side
Light output
Average life Colour temperature
Light distribution Warm-up time
Colour rendering Temperature regime index Comparison with GLS
Type of base Equivalent GLS bulb Colour rendering index Ra
A Black Body radiator has an Ra of 100.
To all intents and purposes a GLS filament lamp has Ra = 100
What is a Black Body?
A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence Light from the Sun What colour is YOUR white? Kelvin colour temperature defined
Simple definition Colour temperature has been described as a method of describing the colour characteristics of light, usually either warm (yellowish) or cool (bluish), and measuring it in degrees of Kelvin (°K). Kelvin colour temperature defined
The Kelvin Colour Temperature scale imagines a black body object (such as a lamp filament) being heated. As the object heats up it begins to glow. As it gets hotter its glowing colour will shift, moving from deep reds, such as a low burning fire would give, to oranges & yellows, all the way up to white hot. Light sources that glow this way are called "incandescent radiators", and the advantage to them is that they have a continuous spectrum Colour temperature and colour rendering
The closer Ra is to 100 the better the colour rendering. High pressure sodium lamps used nowadays in road lighting have an Ra around 30
Low pressure sodium lights have a really poor colour rendering index because they have just two single lines in their spectrum at 589 and 589.1 nm
High pressure metal halide lamps have excellent colour rendering Colour temperature demystified Colour temperature demystified - examples
Light sources other than incandescent lamps have a discontinuous spectrum. The light is emitted at discrete frequencies.
So the colour temperature is defined better as an impression of temperature when compared with daylight Throwing more light on it… A useful guide to buying
Most domestic lamps will be labelled as Cool white; Neutral white, or Warm white
They are now labelled with LUMENS as well as wattage because it is more important
An old-style 60 watt lamp supplied about 800 LUMENS. So it is a good benchmark A few old myths dispelled…
…and the odd anecdote too! Myth #1
Keep hold of as many GLS lamps as you can because all the new lamps are all rubbish
Wrong! GLS lamps only produce light from as little as 2% of the electricity used. The rest is heat. Newer light sources are up to 45% efficient Myth #2
They used to make GLS lamps that only lasted 1,000 hours when they could make lamps that lasted indefinitely
Partly true. The cooler the lamp filament, the longer it lasts. But the efficiency suffers so there is a trade-off. (ANECDOTE #1: The ever-lasting lamp) Myth #3
Compact fluorescent lamps give you eye strain and headaches
Not true. Perhaps you haven’t bought the right colour rendering, or the wattage is too low? Myth #4
Compact fluorescent lamps lose light output very quickly
Not true. In common with all fluorescent lamps the output reduces gradually over time Myth #5
Both compact fluorescent and LED lamps fail well before their stated lifetime
Not true – (now). As with so many things a number of poor quality eastern manufacturers gave the industry a poor reputation. Happily this is now resolved – especially if you buy from a reputable brand The ever-lasting lamp
The lighting industry standardised on the 1,000 hour GLS lamp because there is a real trade-off between filament temperature and lamp life
A hotter filament is more efficient but fails sooner. So why does it fail? Cost of three years lighting in one room
We assume a single 100 watt bulb switched on for an average of 1000 hours in the year 1300
A 1000 hour 100 watt light bulb gives out about 1300 lumens. So the efficiency is about 13 lumens/watt
If the lamp costs, say £1.50p Electricity costs 15p/kilowatt hour So the lamp will cost you £16.50 during it’s life of approximately one year (100 x 0.15 or £15 for the electricity and £1.50p for the lamp!) Cost of three years lighting in one room
1300 1300 1300
In three years you need to buy three lamps The overall cost will be £49.50 We can make lamps that last for 3000 hours
A 3000 hour 100 watt light bulb gives out about 820 820 lumens. So the efficiency is only about 8.2 lumens/watt
If the lamp costs, say £1.50p Electricity costs 15p/kilowatt hour The lamp will cost you £46.50 during it’s life of approximately THREE years (300 x 0.15 or £45 for the electricity and £1.50p for the lamp!) So it looks as if we save!
1300 1300 1300 £49.50 buys you THREE years at 1300 lumens
£46.50 buys you 820 THREE years at 820 lumens
You can save £3.00 and only need to change the bulb once. Good news!! Or is it? Sadly it is a false economy
£49.50 buys you 1300 1300 1300 THREE years at 1300 lumens
£46.50 buys you THREE years, but only at 820 lumens 820 820 To get 1300 lumens you need to have 1.58 times more lamps! Or you could use a 150 watt lamp instead So this would cost you 1.58 times as much electricity The bottom line cost for the same light output
1300 1300 1300 £49.50
820 820 £72.10 So why not make Bright Lights?
A hotter filament produces light much more efficiently, but at the expense of a shorter life. A cooler filament produces more red light and paradoxically therefore looks warmer. The chosen mean lifetime of 1000 hours for a GLS lamp was a compromise. We could produce a much more efficient filament lamp but who wants to change a bulb every month?
But why do lamps fail anyway? From birth to death - II
The coiled coil filament is very fragile and is supported during lamp manufacture by 3 to 7 molybdenum support wires
Inevitably the filament will have inbuilt crystalline defects which will result in a marginally lower cross section at these points
In operation the electric current is constant throughout, but the current density will be greater at the defect, and the filament will run hotter From birth to death - III
The tungsten spiral filament is produced from an ingot of sintered tungsten and drawn though diamond dies to reduce to the ultimate diameter
Tungsten wire is wound as a single coil around a molybdenum mandrel. The coil is then itself would around a larger molybdenum mandrel to form the “coiled coil”. The molybdenum mandrels are removed in an acid bath A coiled coil filament Why a coiled coil anyway?
In a gas-filled lamp the Nitrogen-Argon mixture convects very swiftly past the filament.
But there is a stationary layer immediately next to the filament, discovered by Langmuir (1912).
So making a coiled coil allows a much brighter filament A sublime problem!
Tungsten melts at 3,422 o C
But well before melting it sublimes from the incandescent filament and is deposited on the glass bulb at lower temperatures
As the lamp ages more and more tungsten is deposited on the bulb, which blackens with time
Eventually after being switched on and off many times, and suffering the corresponding stresses of expansion and contraction the filament will finally crack and separate at the crystal defect on switch off Death at the final switch on
At the next (and final) switch on, an arc develops between the two fractured sections of filament
The arc rapidly progresses right back to the two lead-in wire
Arcs have a nasty negative resistance coefficient. So the larger the arc the lower it’s resistance!
To avoid your consumer unit blowing a fuse (literally), the lamp is equipped with a built-in fuse in the base, to cut the arc
This happens in a few milliseconds: all you see is a bright flash and an audible click as the bulb fuse operates Construction of a GLS lamp Thoughts on lighting efficacy - I
TYPE OF LIGHT SOURCE LUMENS/WATT LIFE HOURS Normal gas-filled incandescent lamp (GLS) 8 - 14 1,000 Fluorescent tube (TL) 80-100 4000 Compact fluorescent lamps (CFL) 65-70 8000 High pressure sodium discharge lamps 150 30000 (SON) High pressure metal halide lamps (HPI) 130 Low pressure sodium lamps (SOX) 208 Light emitting diode (LED) 100 - 120 50000 Organic light emitting diode (OLED) 100 40,000?? Latest high efficiency TLED tube 200 ? Thoughts on lighting efficacy - II Thoughts on lighting efficacy - III
Simple fluorescent lamp control circuit
Inductive ballast
AC Mains AC
Fluorescent tube
Cathode Cathode
Starter