Ushio Lighting launched the LED filament lamp in 2008. This device looks remarkably like a classic tungsten filament lamp and has an attractive “retro” look to it which makes it suitable for use in light fittings where the bulb is visible.
The filaments of these lamps consist of a series-connected string of LEDs mounted on a transparent glass or sapphire substrate. This arrangement is known as Chip-On-Glass (COG) and the glass substrate and vertical orientation allows omni-directional light dispersion similar to the incandescent lamp. (Many of the standard LED lamps have a “plastic” look and feel and the electronics and heatsinks restrict light output to 180°.)
The LED “filament” consists of hundreds of LED chips mounted directly onto a transparent glass or saphire substrate instead of the normal metal one – hence the term “chip-on-glass” used to describe these lamps. The glass allows light to be emitted from the rear of the chip as well as the front without shadows or dark zones. As is common practice with many “white” LEDs, the generated light is blue but added phosphors convert some of this into green and red parts of the spectrum to give a broad spectrum “white” light. Variations include filaments with red LEDs added in between the blues.
These lamps are suitable for dimming.
See also Dimmable mains LED bulbs.
