March 10th, 2017 by Chief

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 loosing money, depending on your choices.

 

First of all what is LED?

Traditional filament bulb

LED comes from Light Emitting Diode, and it is a two-lead semiconductor. They were introduced in early 60-s and quickly become regular part in many electronic appliances.
First of all they were replacing standard  incandescent lights, that were usually bigger, had a shorter life, non resilient 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 are extremely wide range of sizes, wattages, and voltages. But back to LEDs….

Red LED

At first LED-s were  used as signalling lights, and due to technology limitations no one even considered them as main light sources. LED`s  were available in yellow, red, and green color at first.
Then in 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 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 left picture of 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 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 wont get damaged either. So you get 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 drawing that explains how to connect it , and some main parts of it.

LEDs came to a significant changes through time, from its most basic design to multi-color diodes, smd diodes, cobs (Chip on board). Here are few examples:

 

 

Now we finally came to a point where we could discuss some everyday lighting uses of LEDs.

core parts of LED bulb

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 bunch of Leds with power driver, external casing, heat sink, light dispenser, and screw base or whatever other type of connector. Once more, device not just a semiconductor. On the left picture is a opened case of the led bulb and I labeled core parts. Board with leds is located on top of Aluminium heat sink, that then spans thru most of the plastic body. 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 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 power driver broken.

E27 base LED

 

Lets 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 frequency of this alternating current should be 50 Hz (You can ignore this)
7W – it means it`s power is 7 Watts. This is smaller light bulb , and by my experience it produces enough light for smaller hallway, but we will come to this many times again.
Power Factor – explanation of my new friend “snakeskin” , regarding power factor:
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 flood light where as a narrow beam angle is a ‘spot’ of light, hence spot light. Led bulb on left picture is declared BA of 180 degrees so it would be a flood light.

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:

Color temperature scale, left is warm white right is cold white.

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 arround  80 CRI, and  100 is 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 manufactures are giving this information, but it is a quite useful and important.

DimmableOld style  : Led lights marked as dimmable are little bit more expensive, lets say if 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 non dimmable circuit, but not vice versa. Do not use non-dimmable led in dimmable circuit since it is not made for it. If you do it you may end up with some of these situations:

 

  1. Led has only two states depending of  position of a potentiometer on your dimmer, and that is on and off. No fine light regulation. Buzzing is optional.
  2. Led is making strange buzzing and wont turn on.
  3. Led is blinking like crazy and buzzing.
  4. Led is dead and wont work anymore.

One more thing to remember : If Led is not marked as dimmable , than for sure it is non-dimmable. Pay attention on what are you buying.
DimmableUpdated 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 back side 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.

Read more of this article »

Posted in Home Tagged with: , , , , , , , , , ,