LED technology – White LEDs
See also: Electronics Weekly’s other roundups of content related to LEDs:
LED technology – White LEDs
LED technology – Coloured LEDs
LED technology – LEDs general
LED technology – LEDs Lighting 1
LED technology – LEDs Lighting 2
LED technology – OLEDs
In well under a decade, LEDs have expanded their role from little red spots which tell you the HiFi is on, to include brilliant white light sources capable of illuminating a room or lighting the road ahead.
Production quality LEDs are now capable of efficiencies of around 70 lm/W, compared with 12 lm/W for incandescent light bulbs, and single die devices are producing over 100 lm.
Here, we present a round up – where the latest relevant stories are dynamically updated – of information related to White LEDs.
History of LEDS
There has been heated argument as to where the actual credit lies, but it is certain that: the company, the man, and the previous research were all necessary.
Nichia initially concentrated on making white LEDs in the classic 5mm and 3mm LED packages, as well as small surface-mount variants.
|Colour coding LED info|
|Driving into the blue|
|Organic – grow your own|
|Into the black?|
|An alternative look at the hues
and shades of LED technology
The Philips-owned Californian company Lumileds introduced the first successful high-power white LEDs, using larger die (1x1mm) for intensity and complex packages to extract the heat generated.
Cree of North Carolina has joined, or even surpassed, Lumileds as the producer of the brightest and most efficient LED die, and Far Eastern companies are not far behind.
How LEDs work
The ‘white’ of white LEDs comes from the narrow-band blue naturally emitted by GaN LEDs, plus a broad spectrum yellow generated by a phosphor coating on the die which absorbs a proportion of the blue and converts it to yellow.
Although this blue die + yellow phosphor approach yields light which appears white, it has little green and almost no red content leading to inferior colour rendering compared with incandescent bulbs and even ‘tri-phosphor’ florescent tubes. ‘Warm white’ LEDs, which include a red-producing phosphor, are an attempt to improve this situation as well as make LEDs illumination more acceptable in living spaces.
LEDs for lighting?
White LED versions of traditional luminaires are already available from several manufacturers, particularly in the MR11 spotlight style.
LED headlights for cars are in the pipeline, notably through the work of Germany’s Osram, which is producing a range of multi-die packages that are close to producing enough light for road illumination. LED bicycle headlights are already available.
Firstly, firms which claim 90 per cent efficiency from LED light sources are making it up. Even the latest ones convert far more electricity to heat than they do to light.
Next, according lighting industry experts, LEDs will remain expensive compared with light bulbs and florescent tubes. And whilst they will increasingly appear in homes and offices, they will almost certainly will not replace florescent tubes in office lighting.
Florescent tubes, at 100 lm/W for the best fittings, are equal in electrical efficiency to the best LEDs.
In the future, large area sheet emitters based on organic LED or AC electroluminescent technology are likely match LEDs in efficiency and to cost far less per lumen to manufacture.
One of these two will probably end up replacing florescent tubes in office lighting and eventually most light bulbs in the home.
In their favour, LEDs are the only real alterative if colour-tuneable accent lighting or colour-tuneable whole-room lighting is required.
And lastly, at the time of writing, large arrays of 5mm LEDs compete well with fewer high-power LEDs in terms of efficiency, cost and heat dissipation.
In the following, we bring together resources from Electronics Weekly and UK and EU governmental bodies to provide detailed reference information about LED technology, specifically white LEDs.
Electronics Weekly news on white LEDs
Most recent news
Previous stories to note
Cree claims white LED record
Cree is claiming a efficacy record for a white power LED. In the lab, a packaged 1x1mm die produced 173 lm of 4,689K white at 350mA and room temperature.
Osram has its brightest ever white LED
Claiming it to be the world’s brightest LED, Osram is to introduce a 250 lm surface mount device early in 2008.
UK consortium to cut white LED costs
A UK consortium had begun work on a £3m Government-funded project to transfer white LED production to cheap silicon wafers.
Lumileds pushes white LED efficiency higher
Lumileds is back in the white LED efficiency race, following a year when Cree and Seoul Semiconductor seemed to pull out a solid lead.
First LED brighter than 50W halogen lamp
Osram Opto Semiconductors has revealed the first LED to achieve more than 1000 lumen – brighter than a 50W halogen lamp, claimed the firm.
White LED specialist Cree signs distributor Arrow
LED lighting specialist Cree has signed a global distribution agreement with Arrow Electronics covering its XLamp products.
White LED from Lamina Ceramics emits 600lumens
Lamina Ceramics claims its Titan range features the only 3,000K, 25W warm white LED light engine available on the market.
Cambridge scientists find reason for dim green LEDs
Researchers at the University of Cambridge may have found the mechanism that makes green LEDs less efficient that other colours, but can’t reveal details.
White LED driver supports 350mA pulse
On Semiconductor has introduced a white LED driver designed to drive high brightness LEDs in torch or flash applications.
LED has brightness of 600mlm
Pacer Components is stocking a range of high-brightness, square, visible LEDs manufactured by Optek Technology .
Good looking viewers support embedded design
For embedded computing applications, such as point-of-sale terminals, display and security systems, a number of suppliers are offering single board computer (SBC) ranges with PC-quality graphics capabilities.
‘Controversial’ theory on InGaN LEDs
Scientists at the University of Cambridge could overturn conventional wisdom on the operation of InGaN LEDs.
White LED reaches 100lm/W
Announced at the US conference Strategies in Light, compound semiconductor firm Cree claims to have achieved 100 lumens per watt from a developmental white LED die.
White LED driver Li-ion suitable
Catalyst Semiconductor has added a high efficiency white LED driver to its family of ICs for panel illumination circuitry. The CAT3604 current regulated charge pump is optimised for use with lithium ion battery powered systems.
LCD firm cuts price with white backlight
Cornwall-based Optoelectronic Manufacturing Corporation (OMC) says it has a range of LED-based white backlights which radically reduce the cost of illuminating LCDs in instrumentation and signs.
Osram sues Nichia over white LED technology
Osram Opto Semiconductors of Germany is suing Nichia over white LED technology.
The lawsuits have been filed in the US and Germany.
The white LED is the least understood of all recent LED developments, according toPhilip Logan, business development manager for supplier Marl International.
Electronics Weekly blogs covering white LEDs
From: Made By Monkeys (Great ideas, Bad execution)
Flashlight Has Dismal Light Output
Those portable shake-to-charge devices seem like a good idea, especially for the battery challenged, but how well does this sort of thing really work?
Clock’s White LEDs Meet an Un-Timely Demise
Bad LEDs don’t die. They just fade away and sometimes exceedingly quickly, like this LED nightlight example.
The Not-So-Bright LED Night Light
In theory, a LED light should last for ten years or so, unlike the typical 4W incandescent lamps used in night lights that seem to burn out in only a few months.
From: Electro Ramblings
LED lighting to take over the world?
A recent round table discussion brought together a group of LED lighting experts, with the talk centred around the possibility of high power LEDs replacing the general purpose market for bulbs.
Electronics Weekly Features on LEDs
Reducing laptop battery drain with LED backlights
Andrew Smith from Power Integrations looks at the benefits and techniques for switching from CCFL to LED backlighting on displays.
White-LED driver operates down to 1.2V supply voltage
Many LED drivers, using both charge pumps and inductors, are available to boost the 1.2 to 2.4V available from single- and dual-cell NiMH (nickel-metal-hydride) batteries to the 3.6V that white LEDs require. However, most of these circuits, such as the Maxim MAX1595, require a minimum input voltage of approximately 2.5V to operate properly.
Electronics Weekly Design Ideas involving LEDs
Video Design Idea: Buck regulator controls white LED with optical feedback
There is much interest in LED-based lighting due to the availability of high-power, high-efficiency white-and other-color-LEDs. Because an LED is a current-controlled device, typical control circuits regulate the current through the LED to maintain uniform intensity.
White-LED driver operates down to 1.2V supply voltage
Many LED drivers, using both charge pumps and inductors, are available to boost the 1.2 to 2.4V available from single- and dual-cell NiMH (nickel-metal-hydride) batteries to the 3.6V that white LEDs require.
Simplified white-LED flasher operates from one cell
Targeting use in portable appliances and products powered by a single cell, this circuit flashes an LED to provide a highly visible warning signal—for example, to indicate power on, battery low, or another eye-catching visual signal.
White-LED driver provides 64-step logarithmic dimming
The circuit of Figure 1 is designed for portable-power applications that require white LEDs with adjustable, logarithmic dimming levels.
Electronics Weekly analysis involving LEDs
Distributors see LED lighting opportunity
Talk of LED lighting applications was once guaranteed to send any self-respecting semiconductor distributor to sleep. Not any more.
Organic and printed electronics to see big growth
The market for printed and potentially printed electronics, including organics, inorganics and composites, will rise from $1.18bn in 2007 to $48.18bn in 2017.
Solid state lighting fires up chip firms
The technology of solid state lighting has its roots in the development of advanced LEDs. As a result it offers designers low voltage drive requirements, cool running, long lifetime reliability, small form-factor and energy saving potential.
Miniature OLED displays explained
Growth prospects for low power microdisplays continue to gain momentum — especially in mobile applications such as music/video players; viewfinders in cameras and video recorders; and in consumer video glasses.
Printed electronics set to be next big thing
Nowadays, the term printed electronics is taken to include thin film electronics that will become printable.