introduction to blue light and the led revolution john mellerio blue light: benefits, hazards and...
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Introduction to Blue Light and the LED revolution
John Mellerio
Blue Light: Benefits, Hazards and Sensitivities - November 2013
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Introduction to Blue Light and the LED revolution
1930 - 1960 Today
Christmas tree lights
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Introduction to Blue Light and the LED revolution
The tungsten lamp gives out energy which varies across the spectrum - a lot of ‘red’, little ‘blue’
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Introduction to Blue Light and the LED revolution
Painting with red paint with the spectral transmittance shown yields a ‘red’ spd
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Introduction to Blue Light and the LED revolution
Painting with blue paint with the spectral transmittance shown yields a ‘blue’ spd
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Introduction to Blue Light and the LED revolution
Painting with blue paint with the spectral transmittance shown yields a ‘blue’ spd
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Introduction to Blue Light and the LED revolution
Allowing for the sensitivity of the eye, blue bulbs are much less effective than the red ones
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Introduction to Blue Light and the LED revolution
SOME PHYSICS
Each photon has an energy with which it can produce effectsThe energy depends on the wavelength, λ, according to the famous equation:
E = h.c/λ
where:
h is Plank’s Constant (6.626 x 10-34 j.s)
c is the velocity of light (3.0 x 108 m.s-1) and
E is the photon energy in joules (which is usually quoted in electron volts by dividing by 1.602 x 10-19)
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Introduction to Blue Light and the LED revolution
Typically the energy nearly doubles between the red and the blue wavelengths
So you’d expect blue photons to be more “lively” in affecting stuff
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Introduction to Blue Light and the LED revolution
In an atom, electrons can only exist in specific orbitals
The closest orbital to the nucleus contains least energy
If a photon has the right energy it will promote that electron up one orbital
If this happens there is absorption but if there is no match the photon passes through: there is no absorption
If an electron falls back to a lower orbital it may release a photon: this is fluorescence
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Introduction to Blue Light and the LED revolution
Excited atoms have energy and do things
So we should expect effects where there is absorption
Looking at tissues, e.g. in the eye, we can predict that tissues might be effected if they absorb the light
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Introduction to Blue Light and the LED revolution
Absorption in the cornea (1), the aqueous (2) and the vitreous (4) is more or less like that of water
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Introduction to Blue Light and the LED revolution
The lens absorbs much blue light and this increases with age
The energy absorbed by the lens may encourage cataract formation
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Introduction to Blue Light and the LED revolution
The retina contains chromophores:photopigmentsmelanincytochromesmacular pigmenthaemoglobin
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Introduction to Blue Light and the LED revolution
In the retina the obvious chromophores are in the photoreceptors
This is the ‘classical’ view
New developments to be revealed later today
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Introduction to Blue Light and the LED revolution
Action spectra show the dose of energy at different wavelengths needed to produce a certain strength of effect, e.g. doubling of enzyme activity or of specified damage
This is photochemical
damage from low intensity sources
Remember where this
peak is when we get to blue
LEDs
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Introduction to Blue Light and the LED revolution
SOURCES OFBLUE LIGHT
Natural sources are nearly all of solar origin:
solar discblue skyreflections from
snow, sand, water
The quality changes with time of day – more later
Other sources:lightning
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Introduction to Blue Light and the LED revolution
SOURCES OFBLUE LIGHT
Natural sources are nearly all of solar origin:
solar discblue skyreflections from
snow, sand, water
The quality changes with time of day – more later
Other sources:lightning
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Introduction to Blue Light and the LED revolution
Artificial sources of blue light are many
As shown earlier, tungsten filament lamps are poor sources of blue but halogen and fluorescent lamps can deliver more blue as can xenon and similar lamps
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Introduction to Blue Light and the LED revolution
Comparison showing ‘black body’ radiation from the sun and some lamp types
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Introduction to Blue Light and the LED revolution
Luminous efficacy is the amount of light you get for every Watt of power usedLamp development is largely driven by seeking the highest luminous efficacyTheoretical max for the ‘perfect’ lamp is 680 lm/W
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Introduction to Blue Light and the LED revolution
Halogen Lamp Tungsten filament doped with, e.g. iodide, allows higher temperature running and greater efficacy
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Introduction to Blue Light and the LED revolution
Fluorescent Lamp Mercury discharge excites a phosphor to give ‘white’ light
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Introduction to Blue Light and the LED revolution
High-Intensity-Discharge or Metal Halide lamp is a form of arc lamp
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Introduction to Blue Light and the LED revolution
Arc in a xenon atmosphere forProjectors systems
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Introduction to Blue Light and the LED revolution
These metal halide lamps are for specialised applications like car headlamps, flood lights, lighting large spaces, etc.
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Introduction to Blue Light and the LED revolution
Lasers can do all kinds of nasty things so we shall not look at them here though they can produce enough blue light to melt Fort Knox
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Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES
How do we getfrom this
to this?
and more . . .
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Introduction to Blue Light and the LED revolution
1907J H Round at Marconi Labs noticed that some crystals used in the early crystal set radios emitted light when an electrical current passed through them – they called this electroluminescence
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
1927Oleg Losev in Russia observed light emission from carborundum point-contact junctions, the first light-emitting diode
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
1962Nick Holonyak at GEC made first, red, LEDs with bright enough emission to use as indicators, etc.Predicted that LEDs will eventually replace incandescent lamps
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
1968First commercial use of mass-produced LEDs was in Hewlett Packard calculators. Did you have one?
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
1972First usable yellow and green LEDs but they are dim
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
1980’sSemiconductor materials become more refined and allow orange, yellow and green LEDs, as well as red, all ten times brighter than the early examples. They became widely used in many applications.
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
1989First LED traffic lights but they don’t catch on immediately as energy conservation was not a consideration then and there were some problems of compatibility with standard specs for colours
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
1993First high brightness blue LEDs which opened the way for developing white LEDs
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
2001First LED pocket torches: these were the first uses for white LEDs
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
2010The first decade of the 21st century saw high power LEDs developed and to date the trend has continued though heat sinking is a major problem.It seems the brightness of LEDs doubles every 3 years.
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
High power LED’s are now found in many applications like LED TV’s, theatre lighting, projector lamps and general and point lighting in the home
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
Highly efficient but coloured light sources are all very well, but the need is for efficient white light to illuminate homes, businesses industry etc.
What can LEDs do?
WHITE LIGHT EMITTING DIODES
There are two main ways of generating white light with LEDs
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Introduction to Blue Light and the LED revolution
The Colour Mixing (CM) SystemUses three LEDs in one casing – one is red, one green and one blue
WHITE LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
Phosphor-Coated (PC) SystemUses a blue LED to excite a phosphor much as a Hg discharge does in a traditional fluorescent lamp
WHITE LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
Colour of White LEDsIn both CM and PC systems the colour can be changed by altering RGB ratios or the nature of the phosphor to obtain warm white, daylight etc.
WHITE LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
Colour Rendering and MetamerismIn both CM and PC systems not all wavelengths are present so strange colour matching may result and appearances are not constant
WHITE LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
DevelopmentGood colour rendering is soughtHigh efficiency is sought and is perhaps the main driving impetus
WHITE LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
DevelopmentHigh efficiency is sought and is the main driving impetus – Dept of Energy (USA) predicts increasing efficacy and has set a target of 266 lm/W for the LED package
WHITE LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
DevelopmentHigh efficiency is sought but in the real World LED packages and luminaires must both be considered
WHITE LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
DevelopmentIf all the lights in the World were LEDs with 200 lm/W luminous efficacy, there would be a saving of 40% of the World’s generating capacity*
WHITE LIGHT EMITTING DIODES
* This controvertial figure is given by Philips – see: http://www.newscenter.philips.com/gb_en/standard/news/press/2013/20130411-philips-creates-the-world-s-most-
energy-efficient-warm-white-led-lamp.wpd#.Unzy-eB21bs
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Introduction to Blue Light and the LED revolution
DangerPC systems encapsulate blue LEDs with peak emissions around the peak of the Blue Light Hazard and the action spectrum for melanopsin suppression and might represent a hazard to the eye and the whole person.We know this because the Daily Mail tells us so.
WHITE LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
POTENTIALWe now have efficient and ubiquitous sources capable of producing high power blue light, and promise of even greater powers and wider applications to come.What is the current state of blue light knowledge and application and where will the future take us?
We hope this meeting helps us to towards understanding the potential of blue light.
LIGHT EMITTING DIODES
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Introduction to Blue Light and the LED revolution
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LIGHT EMITTING DIODES