# Introduction to Blue Light and the LED revolution

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Introduction to Blue Light and the LED revolution
John Mellerio Blue Light: Benefits, Hazards and Sensitivities November 2013

Introduction to Blue Light and the LED revolution
Christmas tree lights Today

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’

Introduction to Blue Light and the LED revolution
Painting with red paint with the spectral transmittance shown yields a ‘red’ spd

Introduction to Blue Light and the LED revolution
Painting with blue paint with the spectral transmittance shown yields a ‘blue’ spd

Introduction to Blue Light and the LED revolution
Painting with blue paint with the spectral transmittance shown yields a ‘blue’ spd

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

Introduction to Blue Light and the LED revolution
SOME PHYSICS Each photon has an energy with which it can produce effects The energy depends on the wavelength, λ, according to the famous equation: E = h.c/λ where: h is Plank’s Constant (6.626 x 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 x 10-19)

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

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

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

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

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

Introduction to Blue Light and the LED revolution
The retina contains chromophores: photopigments melanin cytochromes macular pigment haemoglobin

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

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 Remember where this peak is when we get to blue LEDs This is photochemical damage from low intensity sources

Introduction to Blue Light and the LED revolution
SOURCES OF BLUE LIGHT Natural sources are nearly all of solar origin: solar disc blue sky reflections from snow, sand, water The quality changes with time of day – more later Other sources: lightning

Introduction to Blue Light and the LED revolution
SOURCES OF BLUE LIGHT Natural sources are nearly all of solar origin: solar disc blue sky reflections from snow, sand, water The quality changes with time of day – more later Other sources: lightning

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

Introduction to Blue Light and the LED revolution
Comparison showing ‘black body’ radiation from the sun and some lamp types

Introduction to Blue Light and the LED revolution
70 15 3 Luminous efficacy is the amount of light you get for every Watt of power used Lamp development is largely driven by seeking the highest luminous efficacy Theoretical max for the ‘perfect’ lamp is 680 lm/W

Introduction to Blue Light and the LED revolution
23 Halogen Lamp Tungsten filament doped with, e.g. iodide, allows higher temperature running and greater efficacy

Introduction to Blue Light and the LED revolution
70 Fluorescent Lamp Mercury discharge excites a phosphor to give ‘white’ light

Introduction to Blue Light and the LED revolution
100 High-Intensity-Discharge or Metal Halide lamp is a form of arc lamp

Introduction to Blue Light and the LED revolution
50 Arc in a xenon atmosphere for Projectors systems

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.

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

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES How do we get from this to this? and more . . .

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 1907 J 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

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 1927 Oleg Losev in Russia observed light emission from carborundum point-contact junctions, the first light-emitting diode

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 1962 Nick Holonyak at GEC made first, red, LEDs with bright enough emission to use as indicators, etc. Predicted that LEDs will eventually replace incandescent lamps

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 1968 First commercial use of mass-produced LEDs was in Hewlett Packard calculators. Did you have one?

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 1972 First usable yellow and green LEDs but they are dim

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 1980’s Semiconductor 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.

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 1989 First 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

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 1993 First high brightness blue LEDs which opened the way for developing white LEDs

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 2001 First LED pocket torches: these were the first uses for white LEDs

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 2010 The 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.

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES 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

Introduction to Blue Light and the LED revolution
WHITE LIGHT EMITTING DIODES 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? There are two main ways of generating white light with LEDs

Introduction to Blue Light and the LED revolution
WHITE LIGHT EMITTING DIODES The Colour Mixing (CM) System Uses three LEDs in one casing – one is red, one green and one blue

Introduction to Blue Light and the LED revolution
WHITE LIGHT EMITTING DIODES Phosphor-Coated (PC) System Uses a blue LED to excite a phosphor much as a Hg discharge does in a traditional fluorescent lamp

Introduction to Blue Light and the LED revolution
WHITE LIGHT EMITTING DIODES Colour of White LEDs In 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.

Introduction to Blue Light and the LED revolution
WHITE LIGHT EMITTING DIODES Colour Rendering and Metamerism In both CM and PC systems not all wavelengths are present so strange colour matching may result and appearances are not constant

Introduction to Blue Light and the LED revolution
WHITE LIGHT EMITTING DIODES Development Good colour rendering is sought High efficiency is sought and is perhaps the main driving impetus

Introduction to Blue Light and the LED revolution
WHITE LIGHT EMITTING DIODES Development High 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

Introduction to Blue Light and the LED revolution
WHITE LIGHT EMITTING DIODES Development High efficiency is sought but in the real World LED packages and luminaires must both be considered

Introduction to Blue Light and the LED revolution
WHITE LIGHT EMITTING DIODES Development If 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:

Introduction to Blue Light and the LED revolution
WHITE LIGHT EMITTING DIODES Danger PC 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.

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES POTENTIAL We 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.

Introduction to Blue Light and the LED revolution
LIGHT EMITTING DIODES END

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