Introduction to Blue Light and the LED revolution John Mellerio Blue Light: Benefits, Hazards and...

Introduction to Blue Light and the LED revolution

John Mellerio

Blue Light: Benefits, Hazards and Sensitivities - November 2013


1930 - 1960 Today

Christmas tree lights


The tungsten lamp gives out energy which varies across the spectrum - a lot of ‘red’, little ‘blue’


Painting with red paint with the spectral transmittance shown yields a ‘red’ spd


Painting with blue paint with the spectral transmittance shown yields a ‘blue’ spd


Allowing for the sensitivity of the eye, blue bulbs are much less effective than the red ones


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)


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


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


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


Absorption in the cornea (1), the aqueous (2) and the vitreous (4) is more or less like that of water


The lens absorbs much blue light and this increases with age

The energy absorbed by the lens may encourage cataract formation


The retina contains chromophores:photopigmentsmelanincytochromesmacular pigmenthaemoglobin


In the retina the obvious chromophores are in the photoreceptors

This is the ‘classical’ view

New developments to be revealed later today


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


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


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


Comparison showing ‘black body’ radiation from the sun and some lamp types


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


Halogen Lamp Tungsten filament doped with, e.g. iodide, allows higher temperature running and greater efficacy


Fluorescent Lamp Mercury discharge excites a phosphor to give ‘white’ light


High-Intensity-Discharge or Metal Halide lamp is a form of arc lamp


Arc in a xenon atmosphere forProjectors systems


These metal halide lamps are for specialised applications like car headlamps, flood lights, lighting large spaces, etc.


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


LIGHT EMITTING DIODES

How do we getfrom this

to this?

and more . . .


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



1927Oleg Losev in Russia observed light emission from carborundum point-contact junctions, the first light-emitting diode



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



1968First commercial use of mass-produced LEDs was in Hewlett Packard calculators. Did you have one?



1972First usable yellow and green LEDs but they are dim



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.



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



1993First high brightness blue LEDs which opened the way for developing white LEDs



2001First LED pocket torches: these were the first uses for white LEDs



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.



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



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


The Colour Mixing (CM) SystemUses three LEDs in one casing – one is red, one green and one blue



Phosphor-Coated (PC) SystemUses a blue LED to excite a phosphor much as a Hg discharge does in a traditional fluorescent lamp



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.



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



DevelopmentGood colour rendering is soughtHigh efficiency is sought and is perhaps the main driving impetus



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



DevelopmentHigh efficiency is sought but in the real World LED packages and luminaires must both be considered



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*


* 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


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.



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.



END


Introduction to Blue Light and the LED revolution John Mellerio Blue Light: Benefits, Hazards and...

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Transcript of Introduction to Blue Light and the LED revolution John Mellerio Blue Light: Benefits, Hazards and...