Hugo Holden
Veteran Member
There are certainly a number of myths around about eye strain, used in varoius marketing (perception management) strategies.
The idea of a filter in front of a CRT is a good one though, because it improves the contrast ratio. The color tint is not too important. What happens is that incident light falling on the screen has to pass through the filter layer to get to the Phosphor, then when it is reflected from the phosphor, which has a high albedo, much like the Moon's surface, the light has to pass through the filter layer again to exit the tube face to the observer, so it is filtered twice, unlike the light from the excited phosphor having to pass through the filter only once.
Manufacurers like RCA moved fairly quickly to grey glass (ND filters) filter faces for their CRT's, and they offered many CRT types with a filter faceplate or a clear one as an option.
After a while the faceplates of most CRT's were made of glass thick enough and tough enough not to need a separate safety glass in front of them. By the 1970's nearly all CRT's did not require a separate safety glass and many had tinted glass, and surface treatments to reduce reflections from the shiny glass surface making the surface looke matte finish too.
One of the most impressively dark grey tinted early color CRT's was that used in the IBM 5153 VDU. It looks almost black-ish with the screen not illuminated.
There are many technologies that had to evlove in parallel to make CRT's as wonderful as they had once become, before the world sadly lost it all to economy, weight and space savings making the CRT obsolete in favor of flat screens, but it was a very sad day in my opinion, like the day the music died.
The idea of a filter in front of a CRT is a good one though, because it improves the contrast ratio. The color tint is not too important. What happens is that incident light falling on the screen has to pass through the filter layer to get to the Phosphor, then when it is reflected from the phosphor, which has a high albedo, much like the Moon's surface, the light has to pass through the filter layer again to exit the tube face to the observer, so it is filtered twice, unlike the light from the excited phosphor having to pass through the filter only once.
Manufacurers like RCA moved fairly quickly to grey glass (ND filters) filter faces for their CRT's, and they offered many CRT types with a filter faceplate or a clear one as an option.
After a while the faceplates of most CRT's were made of glass thick enough and tough enough not to need a separate safety glass in front of them. By the 1970's nearly all CRT's did not require a separate safety glass and many had tinted glass, and surface treatments to reduce reflections from the shiny glass surface making the surface looke matte finish too.
One of the most impressively dark grey tinted early color CRT's was that used in the IBM 5153 VDU. It looks almost black-ish with the screen not illuminated.
There are many technologies that had to evlove in parallel to make CRT's as wonderful as they had once become, before the world sadly lost it all to economy, weight and space savings making the CRT obsolete in favor of flat screens, but it was a very sad day in my opinion, like the day the music died.
