Hi All,
Can anyone please explain to me what a GLV is in very simple, layman's terms? I've tried a Google search but the web sites are very technical and for someone who has spent most of his life in a pressroom the descriptions that I have found online are way above my head.
Thanks.
GLV is a plate imaging (CtP) technology.
Grating Light Valve (GLV) is a technology developed by Silicon Light Machines originally introduced to the market at Ipex 2000, with the first platesetters based on GLV available in the Spring of 2003.
There are two central elements to a GLV imaging system: a unique laser module, and a modulator utilizing a GLV ribbon array.
Basically the imaging laser is in the form of a bar just 7 mm long and about 1 mm high. The laser has 39 emitters, and is hermetically sealed in a water-cooled metal housing. (will vary by vendor)
The GLV array itself consists of an array of thousands of microscopic ribbons mounted on a chip about one inch wide. These ribbons are controlled to either reflect or diffract the imaging laser beam, splitting the beam into a very high number of sub-beams, which act as optical channels. Each ribbon is only 4.25 microns wide and 220 microns long, and is spaced in parallel .65 microns apart (there are 25,400 microns to an inch).
GLV-based platesetters typically use 512 laser beams to create laser imaged 10 micron spots on the plate (varies with vendor). The 10 micron spots are then clustered to form halftone dots on the plate.
Generally the GLV CtP devices require that the laser be powered “on” even when not imaging a plate which can limit laser life to approximately 2 years compared to the 4 – 5 years normally expected. At an estimated cost of $25,000 per laser replacement, this can be costly. One compensating factor programmed into some devices is an automatic shutdown of the laser if not used to image for a 5 minute period. Unfortunately, when the laser shuts down, it requires a 5 minute warm-up period following this shutdown.With others the laser diode is “on” but with only enough power to avoid the 5 minute warm-up period, but not enough to affect the life of the laser diodes.
GLV’s achilles heel can be imaging laser swath uniformity, because banding is visible with small differences between pixels. GLV lasers do not have resolution high enough to resist cyclical changes in plates and chemistry and so pixel to pixel densities can easily drift out of balance, making swath banding visible to the eye. GLV vendor’s state reduced specifications for finer screens, because there is not enough exposure latitude in the system to keep the swath uniformly balanced.
I hope that makes some kind of sense.
