A newer LED technology that is referred to in various ways.
Some people also call this simply COB LED, as we read about COB LEDs that one of their more efficient development lines is building the chip on a ceramic substrate. Well, if they build it on glass, glass is also ceramic…
The essence is that COG LED, or Chip On Glass, means LED built on glass. The glass is cut into thin strips, so we can talk about LED filaments. The LED bulbs or candles made this way, at first glance, may seem like a thicker tungsten filament bulb is lit, which is why its most common international name is LED Filament. Some companies, instead of using this long name, refer to it as FiLED.
The driving force behind the development of COG LED was the idea to create an LED light source that mimics a traditional filament. The reason for this is that there is still a demand for light sources that illuminate circularly, practically 360 degrees in space, like a traditional bulb or candle.
This has been solved in two ways so far. The “uglier” solution is the so-called LED corn bulb. Its disadvantage is that it requires a relatively larger number of LEDs, moreover, arranged in space, which involves more labor-intensive production and larger size. The smaller, nicer method is when a cone-shaped PMMA (plexi) element is placed above the flatly arranged LED group or COB LED, ensuring a wider light scattering angle.
However, the complete classic bulb or candle illusion, the retro appearance, can only be provided by this, the LED Filament.
When looking into a lit LED Filament lamp, we get the feeling of looking into a tungsten filament. Of course, this also requires that it does not blind us. Currently (summer 2014), we have 2-4-6-8 filament COG LED candles and bulbs available, with a luminous flux between 210-1000 lumens. The weaker ones can still be looked into – perhaps without an unpleasant blinding sensation, as the resulting light is seen as lines. On a larger surface, unlike a small DIP or SMD LED, where the multiple point light might be more annoying. This is already the subjective part of judging COG LEDs.
From the above data, we can also see that COG LEDs operate with excellent efficiency. Complete LED lamps have an efficiency of 110-115 lumens/Watt, and the LED filaments themselves produce 120-130 lumens/Watt.
The favorable efficiency of COG LED technology is not diminished by the usual opal cover implementation. However, an opal cover is not needed here, as the essence, in addition to the 360-degree illumination angle, is the retro appearance. The opal cover implementation was necessary for three reasons with lamps equipped with various SMD LEDs:
- To reduce the dazzling light of the LED points,
- To cover the not always pleasant appearance of the built-in circuit board, and
- To meet the need for increasing the illumination angle caused by the opal globe surface.
However, developments do not stop at creating the feeling of a traditional light bulb, as COG LED bulbs with cool white and daylight white colors have also appeared. Even though there are no such color temperatures for tungsten filament bulbs, manufacturers are also considering future demands, as opal variants of these will also appear.
Despite the fact that COG LEDs illuminate 360 degrees, it is understandable that less light reaches the ends in the filament direction.
This, however, is usually not a problem, as in a classic chandelier, the bulbs are placed with their sockets down and their tips up, which means that with COB LEDs, the light spreads circularly to the sides, and less light reaches the narrow point on the ceiling. Some manufacturers, feeling this is a problem, place the LED filaments in such a way that each filament line points to a different place, resulting in 4-6 less weak points instead of one light-deficient spot.
According to information found on the internet, this LED format was developed by the Japanese company Ushio in 2008. At that time, they made a light source consisting of 6 filaments, but each filament contained only 3 LED chips. Yes, don’t think that each filament is a single diode. No, each filament has 24-30 diodes strung in series. This 30-chip “tower” was created by the Tavaja company in 2013. So, 24-30 LED chips are applied in series to a 1.5mm thick glass or synthetic sapphire filament, which is coated with phosphor. (All white LEDs are phosphor-coated, regardless of the technology, as it transforms the light into a broad-spectrum visible light.) The color temperature of a LED filament, whether cool or warm white, mainly depends on the original color of the chip series. Red and blue chips are strung on the LED filament. For warm white, red chips are predominant, while with increasing color temperature, the number of blue chips increases, and the phosphor layer makes it white. Of course, the quality of the phosphor also influences how white the white will be and its color rendering index.
Because of the series-connected diodes, a small LED filament typically operates in the 65-80Volt range, so each chip still only gets 2-4Volts.
So, LEDs are built not only on glass slices or filaments (Glass Filament) but also on sapphire filaments (Sapphire Filament).
Neway Lighting also excels in this. The advantage of sapphire is that it is the hardest material after diamond. Although it is not really known why this property is advantageous in the middle of a glass globe, what is outstanding is sapphire’s better thermal conductivity. According to the manufacturer, while this value is only 1.09W/mK for glass, it is 30W/mK for sapphire. And we know that LED lifespan is significantly influenced by heat dissipation. This is an undeniably well-sounding physical parameter, but the construction is the same for both sapphire filament and glass filament LEDs. The LED filaments are enclosed in an inert gas-filled glass globe, as accustomed to with tungsten filament bulbs. It is generally valid that even after 2 hours of use, the surface of a LED filament bulb is only 30-35 degrees Celsius.
These excellent parameters are due to several factors combined. The light generated on the LED filament, whether based on glass or sapphire, can exit circularly without obstruction, not absorbed and thus not converted into heat. Due to the excellent efficiency, the current consumption is lower, and compared to other LED solutions, the heat generation is proportionally the smallest. The lower heat generation and the inert gas-filled globe make unnecessary, for example, an aluminum heatsink design, allowing the production of traditional bulb-shaped glass globes with at least 85% lower consumption LED lamps, which, while their lifespan is 2000 hours, these COG LED lamps have an expected lifespan of over 20,000 hours.