Let There Be Light

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.

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