I used a mesh filter before but now most filters seem to be glass. What is the best material for a filter.
A: Black mesh can be used to make an excellent anti-reflection filter because
reflections from mesh appear to be almost zero. The problem with mesh, however, is resolution. With to-day's high resolution monitors, a mesh filter will most likely create a visual interference pattern called Moire rings which make viewing information on the monitor, for any length of time, especially difficult. This problem is particularly acute with positive displays (black characters on a white background) like Windows®.
Previously, most displays were single phosphor low resolution displays using only one colour and the ring problem wasn't so evident . Also, before, coated glass was extremely expensive and used mainly by the military. But today, with the higher resolution colour displays being used, we believe only a glass filter can truly offer good visual characteristics.
Q2:
There are so many different filters out there, how should I choose a glass screen filter?
A: Our first advice is to make certain you buy a product that offers quality glass with anti-reflection and conductive coatings. Anti-reflection and conductive coatings on glass are manufactured using very expensive and sophisticated equipment and require optically flat glass. The cost of doing this means that the user must pay a little more but we believe it is worth it.
Try to avoid buying the very inexpensive filters made from coloured glass, which some dealers give free with the purchase of a computer system. If the free filter is only coloured glass, ask the dealer to upgrade it to a quality filter with anti-reflection & anti-radiation coatings.
Filter transmission is really a personal choice. People working with monochrome
displays may be able to use a low (30% - 35%) transmission filter with its high contrast enhancement. But as more computer users migrate to using colour monitors with positive displays, we now recommend a fairly high transmission filter, 50% - 60% so that contrast is enhanced without excessive reduction in brightness or colour deepening. We select our glass to be neutral in transmission so that all colours appear with minimal distortion.
Q3:
Why do the prices of glass filters vary so much?
A: Generally, apart from different sizes, mounting methods, and marketing strategies, the better quality the filter glass, the higher the price. Better optical characteristics generally require better quality coatings and so costs are greater. The anti-reflection and conductive coatings on glass are manufactured using very expensive and sophisticated equipment and require optically flat glass. The cost of doing this means that the user must pay a little more but we believe it is worth it.
Q4:
What about the very cheap glass filters, are they any good?
A: There are many inexpensive glass filters on the market; some sell for as little as
US $4.00 - $5.00. It is type that computer stores generally give as a 'gift' to people buying systems. Some of these filters even include a ground cord implying they will provide static and radiation protection.
Usually the very cheap glass filters are made from uncoated, coloured window glass. Although tinted glass will provide additional contrast, generally the reflection is made substantially worse so that operator fatigue develops more quickly as the
operator's eyes & brain must compensate for the added visual confusion. A ground cord attached to one of these filters is useless and is simply a marketing ploy aimed at unknowledgeable users by manufacturers who are, perhaps, less than scrupulous.
Q5:
What about Polarizing filters? Are they that much better?
A: Polarizing filters use a special type of light filter that reduces transmission light by removing light that does not have a prescribed alignment of the electromagnetic
field. Upon passing through the filter twice, there is a cancellation effect so that light with the prescribed alignment essentially removes itself from view. Polarizing filters can be very effective within a certain small range of angles in reducing one type of glare, specular, which makes up a small portion of the glare spectrum. However, outside of this range of angles and for non-specular glare, polarizing filters are no better than other good filters and may not be as good as some testing has shown.
In a research paper published by researchers at Polaroid (Displays, July 1983), their testing showed that a neutral isotropic filter (such as NuVision filters) is actually a little better than a polarizing filter for non-specular glare. Also, generally, non-specular glare is a greater problem than specular glare by a factor of perhaps 10:1 (from MPR2 studies). We suggest you compare according to your environment and buy the better value.
Be aware of false benefits. One well-known manufacturer makes a polarizing filter using a plastic substrate which has a very high reflectance which more than negates the positive aspects of glare reduction by the filter. Unfortunately, many people purchase this filter because of the famous name of the manufacturer but we think they are getting a poor filter.
Q6:
Some filters say they have 10 layers, some say 8 layers, others 4 layers. Some filters are 2-side coated. What is the difference? Are more layers better?
A: The idea of coating anti-reflection layers on the filter glass is to reduce reflection of the glass. The total reflection from clear glass is around 8% - 9% with slightly more coming from the front surface. Reflections from the face of a monitor may be greater because the phosphors also reflect light.
Reflections are caused by the abrupt changing index of refraction from air into the glass as light enters the glass and then from the glass into air as light exits. Anti-reflection coatings are designed to make the transition from air to glass smoother, thereby reducing the amount of light that gets reflected. The design of the coatings depends on the materials used and is very sophisticated - almost an art that is guarded by those who manufacture the coatings.
Usually a filter that is coated with more layers and on 2 sides will be a better filter.
For example, a 4 layer 1-side coated filter might have a total
photopic reflection of about 0.8% while a filter coated on 2 sides with 4 layers each side may have a total photopic reflection of 0.4%. However, when coatings are not well done, 4 layer coatings can be worse than 2 layer coatings.
Q7:
Is safety glass really necessary?
A: It is our opinion that safety glass is not a really necessary feature of screen filters. NuVision could also make screen filters using safety glass. Manufacturers generally use chemically treated or thermally tempered glass for a "safety glass" filter. The process strengthens the glass but also puts the panel under stress. Although safety glass is more difficult to break, if and when it does break, the stress causes the glass to shatter, sometimes with explosive force, into millions of very small pieces. Moreover, the optical properties of the treated glass can be altered so that some distortion is introduced. Because normal glass filters seldom break in any case, we think the possible negatives associated with safety glass render it not worthwhile.
Q8:
Is this radiation dangerous?
A: Some years ago there were suggestions from some scientific research that ELF and VLF radiation might be dangerous to health. Subsequent research showed that the E-field component probably does not penetrate the body but the magnetic field does and so more recent research addressed the magnetic field. The latest (US Government Study, 1996) results, of which we are aware, seem to suggest that these low frequency fields are, in fact, not dangerous to the operators. But, we leave it to the individual to make himself comfortable in this regard.
Q10:
Do filters protect from X-rays & ultra-violet radiation?
A: The emissions of X-ray and ultra-violet radiation by modern monitors are so low
as to be undetectable from background radiation. Thus we feel there is no danger here despite the 'scare' tactics used by some manufacturers and distributors to hype their filters. In any case, glass filters will reduce ultra-violet radiation because glass has that property, but we suspect few people want to use their filter as a sun shade.
Only filters made with glass that contains lead can protect against X-rays. Very few, if any, of today's filters are made using glass that contains sufficient lead for X-ray protection. But then there is no need as the CRT's glass already shields against X-rays as explained above.
Q14:
What are SSI and
TCO?
A: SSI is the abbreviation for the name of a research institute in Sweden that performed some early research into monitor radiation . They developed some recommendations for maximum levels of radiation to be emitted by monitors within a book of ergonomic recommendations called MPR2. These recommendations were not so much health guidelines but rather descriptions of the current possible state of technology.
SSI did provide a filter testing service which attempted to quantify the reduction, by a filter, in electromagnetic field radiation so that different filters could be compared in effectiveness. The test uses a field generator source. Their test is different than an MPR2 test which compares filter effectiveness when placed on an actual monitor.
MPR2 recommendations have been surpassed by MPR3 and TCO recommendations. TCO is another organization that monitors standards in the workplace.
Q15:
