Monthly Archives: April 2014

The history of LED – part 1

When you are talking about the history of some phenomenon, you will end up to the endless question where to start. So is also the case with LED components. As such, light emitting diode is the electrical component which conducts current to only one polarity of voltage, forward voltage, as told in an earlier blog. And this forward voltage applied into this diode produces electrical current that finally creates light. Not every diode produces light, the material has to be suitable in order to produce light. So in addition to having electrically PN diode characteristics, optically component’s material has to be capable of producing light.

This phenomenon, in which electrical current that is driven to the material induces material to emit light, is called electroluminescence. Light can be created also by heating, from chemical reactions, or even by sound, but these are not the topic of this post.

If electroluminescence phenomenon is considered, the first discoveries can be thought to be happened already in the beginning of the 20th century. In 1907 a British experimenter H. J. Round, who was assisting the famous Guglielmo Marconi, found electroluminescence phenomenon using silicon carbide, a compound of silicon and carbon, as light emitting material. He reported his observations to the editors of Electrical World in 1907. The name of the report was “A Note on Carborundum”. Carborundum is a synonym for silicon carbide (SiC). The first LED as such was reported by a Russian Oleg Losev in 1927 in the article “Injected light emission of silicon carbide crystals” in a Russian journal. At that time, no practical use for that kind of component was found. After that several decades passed without significant breakthroughs in LED development.

Caption from a French report "Bichrome Light Emitting Diodes" from 1982

Caption from a French report “Bichrome Light Emitting Diodes” from 1982

If LED development history is thought as the point of view of semiconductor materials, one significant material, or semiconductor alloy, was noticed throughout the years. It was gallium arsenide (GaAs) from which “light” emission could be noticed at infrared wavelengths. Bulk growth of a compound semiconductor GaAs commenced in 1954. Before GaAs, LEDs had been manufactured mainly from SiC. Infrared LEDs and lasers based on GaAs were first reported in 1962 by various groups working in such institutions as RCA, GE, IBM and MIT. By adding aluminium to GaAs, you can get the light output nearer to visible wavelengths; that is from infrared wavelengths to visible red wavelength. Aluminium brings along one problem: it is very susceptible to oxygen that decreases luminescence of the LED.

The decade of breakthrough for light-emitting diodes was definitely 1960’s. During 1961-1962, Texas Instrument workers James R. Biard and Gary Pittman reported GaAs emitting infrared light when electrical current was driven through it. The same men filed a patent in 1962 in which they described a zinc diffused PN-junction GaAs LED which emitted infrared light when the diode was forward biased. James Biard had patents also in many other significant discoveries in semiconductor technology, or microelectronic components, at that time. Several other institutions reported infrared LEDs after that as stated earlier.

Following issuance of Biard’s and Pittman’s patent, Texas Instruments started to develop infrared emitting diodes and finally informed about the commercial LED product, SNX-100, in 1962. But light emitting diode on visible spectrum was still waiting until 1962. Nick Holonyak from General Electric published his article in Applied Physics Letters in December 1962. He had developed red wavelength emitting LED based gallium arsenide phosphide (GaAsP). Thus an era of visible light LED components began. Later M. George Crawford invented the first yellow emitting LED and also improved the brightness of red LEDs remarkably. From those years LED development started from interesting scientific phenomenon and ending to commercial product. Still, there were many obstacles to beat over.

At first, LED were applied mainly in indicator lamps or seven segment displays. LEDs were very expensive at that time and usually they were used in expensive laboratory and electronic measurement equipment. In 1968 a company called Monsanto started to mass-produce visible spectrum LEDs, based on material gallium arsenide phosphide (GaAsP). With this semiconductor alloy, so-called ternary alloy consisted of three elements, red light could be generated. Still, there was enough light only for small indicator lamps. M. George Crawford mentioned earlier in the text was one key technical innovator and manager at Monsanto. Mr. Crawford joined Hewlett Packard after Monsanto and got 2002 National Medal of Technology together with Russell D. Dupuis and Nick Holonyak, for contributions to the development and commercialization of light-emitting diode (LED) technology.

Helkama Flash Cord advertisement from the 80s

Helkama Flash Cord advertisement from the 80s

During the 1970s prices of LED components started to come down. Dr. Jean Hoerni at Fairchild Semiconductor developed planar process for semiconductor chip fabrication and at the same time developed also packaging methods which jointly enabled to reduce costs to produce LED components. This was a very critical step forward in bringing LED also into other application domains than just pure indicator lights in expensive laboratory test equipment. Throughout the years light output increased gradually but there was still something missing that LED could have been thought as a general lighting component that eventually replaces traditional lighting, such as fluorescent tubes, incandescent or halogen lamps, and even high-pressure sodium or metal halide lamps.

How LEDs evolved from being simple indicator light into the lighting component that could be used in everyday general lighting? That you can read in two last parts of the LED history trilogy.

How to choose suitable Constant Current LED driver for your application

Selection of LED Drivers

Selection of LED Drivers

We discussed earlier about the general characteristics of LED drivers. In this post, I’m going to tell you how to choose a right LED driver for your application. LED drivers are divided into two different categories: constant current and constant voltage drivers. But that is not the only thing you have to take into account when selecting the driver. In this post, we are focusing only in constant current drivers.

Constant current drivers are generally used when you need stabile current fed to your LED. With constant current driver, it is easier to manage the right brightness. You can check the datasheet of your light source whether it needs constant current or constant voltage. If it says for example 350mA, then it needs constant current. 12V or 24V means that you need a constant voltage driver.

In this post, we’ll take a look at constant current drivers.

How to choose a constant current driver for your application?

With these step by step instructions, you will find a suitable driver for your luminaire.

Step one: What forward current does your LED need?

As already mentioned, you should find the forward current your LED needs, from the datasheet. For example if your LED needs a current of 350mA, you should try to find a driver with 350mA output current.

Step two: How powerful driver do you need

The power consumption of the LED can also be found from the datasheet or at least it can be calculated with the data in the datasheet. The power consumption can be calculated by multiplying typical driving current value by typical forward voltage value that both can be found in the LED data sheet. Sometimes you can even find the power consumption directly from the datasheet.

Remember that if using multiple LED components, you have to find a driver that can feed all the LED components in your luminaire.

ELT 10W, 500mA LED driver

ELT 10W, 500mA LED driver

Step three: What output voltage range you need from the driver
Again take a look at the datasheet and check the voltage of the LED. If you have multiple LEDs, you should add the voltages together. Then you should find a driver with a voltage range that your LEDs fit into.

Step four: Do you need dimming? And what type of dimming?

A need for dimming is mainly dependent of the specification of your luminaire. If you don’t need dimming, a normal on/off driver is enough for you. If you need dimming, there are many different types of dimming, but that is a topic for another post.

Step five: What are the physical dimensions the driver has to fit into?

You should also consider if there are some limitations for the physical dimensions of the driver. These will obviously have an impact on your driver selection. You will generally find the physical dimensions of the driver from its datasheet.

Step six: What kind of environment the luminaire is used in?

Where is your luminaire designed to be used in? If it is designed to indoor use, then you probably won’t need to think about IP-classification so much. Of course if the luminaire is used in a room with a lot of dust or moisture, this has to be taken into account.

ELT 60W, 700mA, IP20 driver

ELT 60W, 700mA, IP20 driver

IP20 class drivers it means that this driver can be used in indoor lighting applications but hardly stands harsh conditions in outdoor lighting unless the luminaire itself is waterproof thus protecting the driver.

But when designing a luminaire to outdoor use, then you should check that that the driver has good enough IP-class.

Usually IP67 drivers are heavier in weight, driver electronics is molded with plastic (e.g. potted) and the electrical throughputs of the wires both on primary voltage and the secondary voltage side are sealed with required protection against moisture.

ELT 10W, 350mA, IP67 driver

ELT 10W, 350mA, IP67 driver

Step seven: Approvals, is the driver suited for European or American standards?

Does the driver have any approvals? And are the approvals for Europe (ENEC) or America (UL). This can generally be found from the datasheet of the driver.

So there you have it. With these steps you should be able to find a suitable LED driver for your application. If you don’t, please leave a comment or contact me directly.

You can also use our Light Builder to select a driver.