Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!dali.cs.montana.edu!milton!hlab From: kilian@poplar.cray.com (Alan Kilian) Newsgroups: sci.virtual-worlds Subject: VR hardware safety response Message-ID: <1991Jun5.031158.15999@milton.u.washington.edu> Date: 5 Jun 91 02:59:12 GMT Sender: hlab@milton.u.washington.edu (Human Int. Technology Lab) Organization: University of Washington Lines: 96 Approved: cyberoid@milton.u.washington.edu galt@hellgate.utah.edu (Greg Alt) Says: > It seems that CRT's are a possible health risk and should not be used > right up against your eyes for a long time. That debate rages on and until I see some more articles I am not going to put any CRT based displays right in front of my eyes. The "Light valve" designs seem much safer in the mean time. > but what about LCD screens? > While there is little or no radiation, it is still looking at something > only a few inches away from your face. I would think this is not good > and could cause some pretty bad eyestrain. Well, not really. The screen is only a few inches from your face but it is optically much farther away. Some people say "Optical infinity" but it seems more like one meter or so to me. > I am nearsighted, and my glasses have the effect of bringing objects > about a foot from my eyes. I don't really think that that is correct. When you see an object that is "really" 2 meters away does it look like it's only a foot from your eye? (Sorry about the mixed units there). I don't think it does. I have -4.75 diopters correction so my "optical infinity" is only 1/4.75 meters in front of my eye so optically my glasses take objects at infinity and translate them to 1/4.75 meters away, but the two corrections (My eyes are +4.75 and my glasses are -4.75) cancel and I can see just like "normal" people. Well anyway, I forgot what my point was. > I wonder what the effect of the optics are on the LCD screen. I would > hope they take the screen farther away from your eyes and enlarge it, They do make the screen seem farther away but they don't really "enlarge" it. Well they do, but not really. it's like this: /| / | / | / | / | / | /| | / | | / | | Your eye-----> . | | You are looking this way ---> \ | | \ | | \| | \ | \ | ^ \ | | \ | | \ | | \| | | ^ | | The "real" position ---+ +--- The optical position of the screen. ofn the LCD screen So the screen "looks" bigger because you think it's farther away, but it does not subtend a greater solid angle so it's not really "enlarged" > but does anyone know the sort of lenses that would be used? You could use a 8cm focal length lens 8cm from the screen to get the screen to be at optical infinity. > It would be very good if it would have the effect of taking the picture > out to infinite... > > Also, in a couple weeks, I will start to work on a simple 3D graphics > system that has perspective views. I will write it in Turbo C, and > I will post it (or send it to the new cheap-VR ftp site). I plan on > using a hierarchical structure similar to PHIGS, and it will be flexible > with color and depth cueing. If anyone has comments or suggestions, > please email me... I plan on not supporting lights, but I think I > will leave some hooks to allow expansion... What are you trying to get? There are many public domain 3D graphics systems out there that support all of this. If you are trying to really understand 3D than this is the way to go but if you just want to be able to draw things get something like the simple phigs package from brown university. (Mail to spr@cs.brown.edu because I can't find the IP number) they have a PHIGS package that runs with the X-Window system. -Alan Kilian -Alan Kilian kilian@cray.com 612.683.5499 Cray Research, Inc. | "The Fragile X Syndrome may me the most 655 F Lone Oak Drive | frequent cause of inherited mental Eagan MN, 55121 | retardation". Science 24-May-1991 PP1097