“The science of today is the technology of tomorrow.”
— Edward Teller
Here are few thoughts about led lights, what are they, how do they work, why do we need them, and what to expect from them. There will also be a buyers guide, or should we say some advice about what types should you avoid purchasing. Led lights can be quite expensive, and electricity prices are also climbing, so you could end up saving or losing money, depending on your choices.
The LED comes from Light Emitting Diode, and it is a two-lead semiconductor. They were introduced in the early 60-s and quickly become a regular part of many electronic appliances.
First of all, they were replacing standard incandescent lights, that were usually bigger, had a shorter life, nonresilient to vibrations and most off all more power-consuming.
The incandescent light bulb or lamp is a source of electric light that works by incandescence, which is the emission of light caused by heating the filament. There is an extremely wide range of sizes, wattages, and voltages. But back to LEDs…
At first, LED-s were used as signaling lights, and due to technical limitations, no one even considered them as main light sources. LED`s were available in yellow, red, and green color at first.
Then in the early 1990-s, professors Isamu Akasaki, Hiroshi Amano and Shuji Nakamura made the first blue LEDs.
Later this enabled a new generation of bright, energy-efficient white lamps, as well as color LED screens.
So, how to use LED? Basically you need DC power source (DC stands for Direct Current) matching voltage required by LED, and a resistor connected in serial is for over-current protection. It has two leads called Cathode or – and Anode or +.
You can notice that one of the leads on the left picture of the red led is longer. That is Anode and it is a way that manufacturer tells you “that lead goes to +” .There is also a flat spot on the bottom of the led casing where other lead comes out, and that is the way to tell you that that lead goes to -. Why two markings you would ask? Well in electronics there are a lot of wise guys with all different sorts of tools, and sometimes leads get a final touch by cutters, so without this second marking, you would end up not knowing what is + and what is -. Well even if you do not know anode and cathode it is not a trouble, as if connected wrong LED will not work, but won’t get damaged either. So you get a 50% chance to connect it right, and if there is no light coming out of it, just reverse the polarity.
Here on this next illustration is a drawing that explains how to connect it, and some main parts of it.
LEDs came to significant changes through time, from its most basic design to multi-color diodes, smd diodes, cobs (Chip on board). Here are a few examples:
From now on we will be talking about Led or Led bulb as a complete device, not just a semiconductor. In this case, it is a bunch of Leds with power driver, external casing, heat sink, light dispenser, and screw base or whatever another type of connector. Once more, the device not just a semiconductor. On the left picture is an opened case of the led bulb and I labeled core parts. The board with LEDs is located on top of the Aluminium heat sink, which then spans thru most of the plastic body. The power driver converts 220V AC to DC voltage necessary for LEDs to work. This design is good for LEDs since they have some decent cooling, but the power driver is in trouble since by itself it is heating much, and LEDs are adding fuel to its flames by adding their heat to this closed casing. As a result, you soon get a power driver broken.
Let’s observe markings from this E27 (Edison screw light base size 27) Led Bulb
AC – it means that it is for alternating current only
220V – it means that it`s operational voltage is 220 Volts so it is for Europe
50 Hz – it means that the frequency of this alternating current should be 50 Hz (You can ignore this)
7W – it means it`s power is 7 Watts. This is a smaller light bulb, and by my experience, it produces enough light for a smaller hallway, but we will come to this many times again.
Power Factor – explanation of my new friend “snakeskin” , regarding power factor:
The power factor has to do with the phase or timing of the AC current and how it is affected by the power supply. It’s kind of hard to describe because it involves real numbers (as in the square root of -1) and understanding how power companies generate and supply power. The important thing for you is it is not a rating of the efficacy of the fixture
Beam angle – first of all, beam angles are not used consistently by light bulb manufacturers. A wide beam angle ‘floods’ an area with light and is called a floodlight whereas a narrow beam angle is a ‘spot’ of light, hence spot light. The led bulb on the left picture is declared a BA of 180 degrees so it would be a floodlight.
6500 K – Color temperature in Kelvins – it means that it is between warm and cold white. Here is an example scale so you can get some basic idea:
There are also some other things to observe when purchasing LEDs for your lighting:
CRI – A color rendering index is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with an ideal or natural light source. TheCRI is determined by the light source’s spectrum. Typical LEDs have around 80 CRI, and 100 is an index of (daylight).
Lumen output – It is related to the brightness, which is the lumen output of an object in a given spectral region. Shorter to say more Lumens = more light.
Not many of the manufacturers are giving this information, but it is quite useful and important.
Dimmable – Old style: Led lights marked as dimmable are a little bit more expensive, let’s say if the non-dimmable led is 8 $ than same led but dimmable version would be 9 – 10 $. What does it mean? It means that you can manipulate its brightness by regulating circuit. One more important thing to remember is that dimmable LEDs can work in a non-dimmable circuit, but not vice versa. Do not use non-dimmable led in the dimmable circuit since it is not made for it. If you do it you may end up with some of these situations:
One more thing to remember: If Led is not marked as dimmable, than for sure it is non-dimmable. Pay attention to what are you buying.
Dimmable – Updated information from our friend Snakesign :
There are two types of phase dimming available on the market. Old style triac dimmers cut the front part of the AC sine wave to reduce delivered power. This is called Triac, forward phase, or magnetic low voltage (MLV) dimming. Because this induces a large current in the power supply when you go from 0 to some high part on the sine wave a new more modern dimmer was created. This is trailing edge, reverse phase, or electronic low voltage (ELV) dimming. It cuts out the backside of the sine wave to reduce delivered power. LED’s will respond differently to both types of dimmers. There is also a lot of difference between a shitty $10 dimmer from Home Depot and a $75 dimmer from Lutron, even in the same dimming class. There is also some difference depending on how heavily the line is loaded. So compatibility has to be determined on an almost case by case basis.