Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!floyd!harpo!decvax!decwrl!amd70!fortune!wdl1!jbn From: jbn@wdl1.UUCP (John B. Nagle) Newsgroups: net.micro Subject: On front panels and indicators Message-ID: <331@wdl1.UUCP> Date: Wed, 20-Jun-84 16:40:31 EDT Article-I.D.: wdl1.331 Posted: Wed Jun 20 16:40:31 1984 Date-Received: Fri, 22-Jun-84 06:17:35 EDT Lines: 33 There have been some discussions on front panels, switches and indicators. There is a tendency in the computer industry to make all lamps the same color. At one time LEDs came only in red, and there seem to be engineers who haven't heard that they now come in at least red, yellow, blue, green, and white. There are too many boxes around with rows of cryptically-lebelled LEDs. This is wrong. There are ANSI standards for indicator colors. They are followed rigorously in aircraft instrumentation and heavy industry. IBM and DEC tend to follow these standards. Many of the other vendors don't, to their customers' annoyance. So here are the standard colors and their usages. RED Indicates trouble. When a red lamp is illuminated, the operator should be taking action to make it go out. In normal operation, no red lamp should ever be illuminated. YELLOW Indicates an abnormal situation. When a yellow lamp is illuminated, the operator should be aware of the abnormal situation but it is not necessary that all yellow lamps be out in normal operation. GREEN Indicates a normal situation. WHITE Indicates a status, typically ON. BLUE An alternative for white, used when a second status indication is needed. As can be seen from the above, red should be used sparingly and never by default. When in doubt, use white. (Yes, there are white LEDs). When there are lots of boxes with lots of lamps, and everybody follows the rules, a quick glance tells you if anything needs attention. And that, of course, is the point.