ANSI/VITA 40-2003

ANSI/VITA 40-2003

Abstract: This human factors engineering standard defines the colors, behaviors, placement, and labeling of status indicators for boards, field replaceable units, and enclosures in the computer industry. It is generally applicable to all types of products and components that employ lights to convey status information to the user. It is based on existing US and international human factors standards, guidelines, and engineering practices and was developed and approved as an official American National Standards Institute (ANSI) standard through the ANSI-accredited VMEbus International Trade Association (VITA) [] Standards Organization (VSO) [] in 2003. Copies of the full standard may be ordered directly from VSO. [] at For a summary of the standard's requirements, see "Putting It All Together" (section 6) below.


This standard was developed to address the problem of inconsistency across products and vendors in the use of colors, behaviors, placement, and labeling of status indicators employed in the computer industry. This inconsistency increases the probability of human error in quickly and accurately interpreting the operational status of a component or system. Operational and service errors caused by incorrect interpretation of status (e.g., removing the wrong hard drive) can be enormously costly if they cause the loss of availability of a computer system upon which an enterprise depends. Losses of sales to an e-commerce site in excess $1M per minute are easily possible. ANSI/VITA 40-2003 was created to provide intuitive and consistent status indicator implementations based on existing human factors and ergonomic standards, guidelines, and engineering "best practices". Where conflicts existed among different standards and guidelines, every effort was made to choose the most universally accepted practice. In some cases, usability research was conducted to validate aspects of the ANSI/VITA 40-2003 standard.

General Principles

The standard was designed to be as simple as possible and to use consistent syntax for colors and behaviors. For example, green is only used to indicate benign, or "normal" conditions, and amber is only used to indicate faults or conditions requiring user attention. Similarly, behaviors such as different blink rates are very limited and clearly distinguishable. The combination of colors and behaviors forms a simple, consistent, and easily understood "language" for status indicators.

The meanings assigned to each indicator color (i.e., green, amber, blue, white, and red) are mutually exclusive. Similarly, the meanings assigned to each indicator behavior (e.g., SLOW BLINK, STEADY ON, OFF, etc.) are also mutually exclusive. Therefore, any combination of colors and behaviors visible at any one time merely represents a series of discrete messages, one per color (e.g., STEADY ON green means "the system is functioning"; SLOW BLINK amber means "a new service action is required"; when both are illuminated at the same time the message is therefore: "the system is delivering service but there is a fault condition present that needs attention").

Significantly, ANSI/VITA 40-2003 does not assign particular meanings to specific combinations of colors and behaviors. Such implementations are seldom intuitive to the user and therefore have a high probability of misinterpretation without documentation in the form of detailed labeling or other immediately available interpretation aids.

The meanings used in this standard for colors and behavioral states of indicators were derived from a variety of existing standards, guidelines, and supporting research studies. Every effort was made to find common ground among the various standards and guidelines. Wherever possible, key standards are cited in support of statements in ANSI/VITA 40-2003. Most of these standards are based on extensive review and research, some with history going back 50 years or more (e.g., MIL-STD-1472).

Practical Application of ANSI/VITA 40-2003

Not all status indicator colors and behaviors are required for every application situation. The specific application of colors and behaviors to indicators should be based on the status information and feedback requirements of service personnel when performing service actions on the product (this application strategy is derived from from IEC 73, see references below).

As early as possible in the product design process, the product development team should develop an operational concept for the product. This concept should consider operational environments, technology, the expected skill level of service personnel, user tasks, diagnostic capability, determine what display information is required to minimize the probability of human error during servicing operations and to reduce the mean time to repair (MTTR). This analysis should yield a list of required indicator colors and their behaviors for the product. Since the application of indicators to a product is based on an analysis specific to that product, not every product will have the same set of indicators and behaviors. However, those indicators that are present must comply with this standard. For example, if a board is not hot swappable, there is no need for it to have a "Ready to Remove" indicator.


ANSI/VITA 40-2003 allows only five different colors: green, amber, blue, white, and red. Colors were chosen based on three criteria: 1) conventional standard meanings, 2) discriminability among colors, and 3) common availability of LED colors.


GREEN is commonly used to denote normal operating conditions (e.g., system delivering service). Many standards specify meanings for green. For example, MIL-STD-1472F section states that "green shall be used to indicate that the monitored equipment is in tolerance or a condition is satisfactory and that it is all right to proceed (e.g., "in-tolerance", "ready", "function activated)". Similarly, Telcordia Standard GR-2914-CORE states that, "green shall indicate satisfactory operation, active condition, or completion of a process or procedure." International standard CEI IEC 73 section assigns the meaning to green as a "normal" state of equipment or a "normal" condition of a process. The ANSI/VITA 40-2003 meaning of green is: "OK", "normal", "satisfactory operation", "active", or "in service". It indicates satisfactory operation, active condition, or completion of a process or procedure.

AMBER is commonly used to denote faults or conditions of which a user should be made aware (e.g., a cooling fan failure). Yellow or amber is commonly used to denote that the system or component requires attention or a service action, or that something is not functioning normally. MIL-STD-1472 states that, "yellow shall be used to advise an operator that a condition exists which is marginal" or " alert the operator to situations where caution, recheck, or unexpected delay is necessary." Telcordia GR-2914-CORE states that, "yellow or amber shall indicate minor failure, caution, warning, temporary malfunction, or state for which the craftsperson should use caution." International standard CEI IEC 73 section assigns the meaning to yellow as an "abnormal" state of equipment or an "abnormal" condition of a process. The intent of yellow in this standard is to provide indication that a problem exists somewhere on the component or system. The ANSI/VITA 40-2003 meaning of amber is: "attention" or "service action required". Yellow or amber indicates a minor failure, caution, warning, or temporary malfunction, or state for which the service person should use caution.

BLUE is used in ANSI/VITA 40-2003 to provide an active indication that it is safe to perform a service action (e.g., remove a component) while the system is running, i.e., there will be no loss or unacceptable degradation of service if the service action is performed. In this standard, blue is typically applied to hot swappable components to indicate when they are save to remove. The requirement for an active, rather than passive, indication for safe removal is a critical distinction and is one of the most important features of this standard. "Active" means that there is a distinct indicator that comes "on" to indicate "service action allowed" as opposed to having an indicator go "off" to indicate "service action allowed". An active indicator is unambiguous, whereas a passive indicator introduces uncertainty and ambiguity about whether or not it is OK to take a service action that could have major consequences (e.g., the indicator could be "off" due to a lamp failure). MIL-STD-1472F states that, "...the absence or loss of a signal or visual indication shall not be used to indicate a "ready" or "in tolerance" condition...". The provision of an active "OK to remove" indicator is a key requirement of Telcordia Standard GR-2914-CORE. Rule R5-1 states that, "There shall be one Light-Emitting Diode (LED) on each FRU (field replaceable unit), whose primary function shall be to indicate that the FRU can be pulled from the (network equipment or "NE") without interrupting any service (i.e., NE management or traffic) or causing damage to equipment or physical harm to the technician."

The choice of the color blue for this indicator is based on the need to provide a color that is technically feasible, distinguishable in appearance from the other colors used in this standard, and has no meaning stereotype that contradicts the message intended. MIL-STD-1472F allows use of blue as an "advisory light". CEI IEC 73 allows use of blue for "mandatory significance", i.e., to indicate something that is associated with a required action. In contrast, Telcordia GR-2914-GR uses red for the "OK to remove" indicator, but red also has the meaning in the telecommunications environment of "out of service". A research study at a computer systems company showed that system administrators interpreted red as meaning "stop" and expressed a strong preference for a blue rather than red to indicate that it was OK to proceed with a service action. The GR-2914-CORE project manager, in a personal communication, stated that the key requirement of GR-2914-CORE was the provision of an active indicator and that the color used was of less importance. Finally, blue is presently used in the electronic board industry to indicate that a board is unclaimed by the system and is therefore "OK to remove" or that a "service action is allowed" (e.g., see “Live Insertion for VME64x”, VITA 1.4-199x, (latest draft) and “CompactPCI Specification” PICMG 2.1 R1.0 (full hot swap) ).

WHITE is used in ANSI/VITA 40-2003 to provide an aid to locating a particular system or subassembly. This function is especially valuable for enclosures installed in environments where there may be numerous identical units in operation. In order to make the locator indicator be more noticeable, it uses a distinctive FAST BLINK that is very different from the SLOW BLINK used by other indicators. The ANSI/VITA 40-2003 meaning of white is "here I am" or "this is the item being sought" or "Unit identification (UID)". CEI IEC 73 has no meaning assigned to white. White indicates a neutral condition that implies nothing about the success or failure of system operations.

RED is commonly used to denote "out of service" or warn of danger or a significant possible personal injury hazard. It is used sparingly because it represents an extreme hazard usually associated with safety issues (e.g., personal injury hazards on factory equipment) or significant outages (e.g., out of service alarms in telco equipment). Red indicates a critical or major failure, error, or danger. Use of red may be problematic in environments where red has special meaning. For example, a red warning indicator in an industrial environment may be used to alert personnel to life threatening conditions, physical danger, fire, or emergency exits. MIL-STD-1472F assigns the meaning, " go, error, failure, malfunction". CEI IEC 73 defines red as "emergency" or "dangerous condition". CEI IEC 60950-1 states that red "... is permitted provided that it is clear that safety is not involved." When red is used in the context of this standard, it must have a distinct and unambiguous meaning in relation to the other colors. The ANSI/VITA 40-2003 meaning of red is "out of service", "major fault", or "critical fault".


Human factors research on color discrimination has mapped the just noticeable differences of human perception between colors and these have been mapped to the CIE 1931 Chromaticity Chart. The objective of the color choices for ANSI/VITA 40-2003 was for them to be separated from one another by approximately 3-7 color steps of 3 just-noticeable-differences (JNDs) each, according to published color research studies (See ref.: Boff, KR and Lincoln, JE 1988 Engineering Data Compendium: Human Perception and Performance, Section 1.704, pp 332-333. AAMRL, Wright-Paterson AFB, OH). This strategy had the added effect of minimizing the problems of color discrimination by most color blind individuals. These particular colors were also selected because they are technically feasible and commercially available. The definition of white is problematic because various lamp manufacturers define it differently and generate it by blending values for R, G, and B. Therefore, since the strategy of selecting color by dominant wavelength can't apply to white, the standard describes an operational test to verify that users see the color as white.


All colors cited in ANSI/VITA 40-2003 are readily available in a variety of electronic packages (e.g., surface mount, soldered leads, etc.) from a variety of vendors. When implementing the standard, color choices can reasonably be based on the vendors' published dominant wavelengths for each part. Vendor names for colors are inconsistent and therefore should NOT be used when selecting parts.

Color Dominant Wavelength or Color Description Meanings
630 nm (615 nm to 650 nm allowable) out of service
approx x=0.31, y=0.32 on the CIE 1931 Chromaticity Diagram locate or unit identification function
470 nm (445 nm to 480 nm allowable) ready to service; unclaimed by system; ready to remove
590 nm (583 nm to 593 nm allowable) fault; service action required; warning
525 nm (505 nm to 535 nm allowable) OK; operational


Under ANSI/VITA 40-2003, status indicators may only have a very limited number of different behaviors. All behaviors are designed to be easily and unambiguously discriminable from one another, based on human factors standards. For example human factors standards state that humans have a limited ability to discriminate between different blink rates. International standard IEC 73, paragraph 333 states that in order for users to discriminate between two different blink rates they must differ by at least a ratio of 1:2.5. Hence, if a blink rate of 1 Hz is used, the next possible higher blink rate that users can discriminate reliably would be 2.5 Hz. The table below lists the behaviors that are allowed by ANSI/VITA 40-2003.

Behavior Definition Typical Use
light not illuminated not operational
light illuminated system or component operational, e.g., delivering service
1 Hz repeating sequence with equal ON and OFF time on-going activity, e.g., system booting, POST, transition from one mode to another, etc.
4 Hz repeating sequence with equal ON and OFF time attention-getting location aid or unit ID indication, e.g., unit ID light blinking
repeating sequence having a 3-second duration, consisting of a brief (0.1 second) ON flash followed by a long OFF period (2.9 seconds) system or component in standby mode, e.g., a cell phone waiting to receive a call; hot spare waiting to be used, etc.
indicator is ON but goes OFF during periods of activity disk drive read and write activity; comm port transmit and receive activity; flickering rate is commensurate with the activity

Putting It All Together: Colors, Behaviors, and Meanings Assigned to Indicators

The following table summarizes the behaviors and meanings assigned to each color by the ANSI/VITA 40-2003 standard.

Colors Permitted Behaviors Meanings Comments
STEADY ON "out of service" not recommended for use except in special environments, such as telecommunications centers
FAST BLINK "locate", "here I am", "Unit ID" FAST BLINK is used only for this attention-getting function
STEADY ON "service action allowed", "ready to remove from service", "unclaimed" only used for components that require a specific action to make them safe to remove while the system is running; ideally when blue comes ON all other indicators become OFF
SLOW BLINK a new (unacknowledged) event requiring a service action has been detected the purpose of this behavior is to make it possible to distinguish new faults from old faults
STEADY ON the service action required event has been acknowledged but the problem still exists amber stays on until the problem has been corrected
STANDBY BLINK the system or component is running at a minimum level and is ready to be quickly revived to full function e.g, a "hot spare" in standby mode
STEADY ON normal system or component function this is NOT a power indication; green means the system is operational and delivering service
SLOW BLINK a normal transitory activity is taking place e.g., boot process underway, shutdown in progress, switching modes, etc.
FEEDBACK FLASH a normal activity is taking place for which direct, proportional feedback is desirable e.g., read and write activity on a hard drive; communication transmit/receive activity on a communications port

Indicator Icons, Labeling, and Placement

Indicators should be placed so they can be seen from any normally expected user eye position for the typical task requiring their use. Ideally, indicators should be visible in all directions at a side angle 60 degrees off of a line that is perpendicular to the indicator mounting surface and passing through the center of the indicator (i.e, forming a 120 degree field of view cone around the indicator). Labels should be placed above or to the right of the indicator. ANSI/VITA 40-2003 specifies icons and ideal spacing for each indicator type.

The proper indicator placement order from top to bottom is: red, white, (space), blue, amber, green and from left to right is: red, white, (space) blue, amber, green.

The image below shows the icons specified by ANSI/VITA 40-2003.

Luminance and Illumination

ANSI/VITA 40-2003 does not include specific recommendations for luminance of status indicators, although this may be added in an upcoming update of the standard (see "Future Development" below). The standard does contain several recommendations and observations about luminance and illumination. Adjacent indicators should be discernible from one another and not obscured by over bright "blooming" of one light. Light from one indicator should be shielded from an adjacent indicator so that the indicator that is "off" does not appear to be "on". Indicator luminance should match the requirements imposed by environmental conditions: bright in brightly lit environments but dimmer in darker environments. Finally, all indicators on a single component or system should appear to have roughly equal brightness. This means the measured luminance values for different colors may vary because of variances in human sensitivity to color.

Prioritization by Indicator Size

4mm = overall system or enclosure summary status (e.g., unit delivering service)

3mm = removable component status (e.g., power supply status)

2mm = supplemental information (e.g., temperature)

Test Features

ANSI/VITA 40-2003 recommends implementation of three test features. These can be very useful because they can reduce the mean time to make repairs and minimize the probability of service errors by providing service personnel with timely and unambiguous confirmation that the system, components, and indicators are functional. Tests may also be very useful in quality control testing of indicators during manufacturing.

Power-on testing - If the service indicators are used for power-on testing, every indicator in the set of indicators on each board or component should SLOW BLINK in unison for no less than 1 second and no more than 5 seconds. If multiple boards in a system enclosure are tested at power-on, it is recommended that the test be conducted in ordered sequence throughout the enclosure from left to right, top to bottom, then front to back.

Board insertion testing - Boards and components should self-test on insertion to provide immediate feedback that the board or component has been inserted correctly. If the insertion test is implemented, every indicator in the set of indicators on the board or FRU should SLOW BLINK in unison for no less than 1 second and no more than 5 seconds.

Lamp inspection testing - Boards and components should incorporate a lamp inspection test capability so that it is possible to confirm that no lamps are burned out or otherwise non-functional. Lamp tests should be implemented through a momentary push button on the enclosure that, while depressed, illuminates all the lamps on that side of the enclosure, in unison. Lamp tests may also be performed through a software command, but these tests should have a time-out function so that the indicators return to their current valid state in less than 30 seconds.

Future Development

ANSI requires that all standards be reviewed every five years. Therefore, AV40 will be reviewed by VSO by the end of 2008. Based on industry experience, several improvements to the standard are being contemplated. Among them are changes to the permitted color ranges to ensure more visual consistency, addition of luminance recommendations for each color, and the addition of several behaviors to indicate additional functions (e.g., diagnostic mode, predicted failure) or alternate methods of showing existing functions (e.g., "locate" when no dedicated locate indicator is available).

References Used in Developing ANSI/VITA 40-2003

CIE 107-1994, Review of the Official Recommendations of the CIE for the Colours of Signal Lights

CEI IEC 60950-1 Information Technology Equipment - Safety

Engineering Data Compendium, Human Perception and Performance, Vol. I. Boff, JR and Lincoln, JE, Eds., 1988, AAMRL, Wright-Paterson AFB, OH

CEI IEC 73, Basic and Safety Principles for Man-Machine Interface, Marking, and Identification

IEEE 1101-1-1998, Standard for Mechanical Core Specifications for Microcomputers Using IEC 60603-2 Connectors

IEEE 1101-10-1996, Standard for Additional Mechanical Specifications for Microcomputers Using IEEE Std 1101.1-1991 Equipment Practice

Ishihara Test for Color Blindness

MIL-STD-1472F, Dept. of Defense, Design Criteria Standard, Human Engineering

PICMG 2.0 R1.0 (full hot swap) CompactPCI Hot Swap Specification

Telcordia Standard GR-2914-CORE, Human Factors Requirements for Equipment to Improve Network Reliability

Telcordia Standard GR-474-CORE, Network Maintenance: Alarm and Control for Network Elements

Telcordia Standard GR-499-CORE, TSGR: Common Requirements

Website concerned with ANSI/VITA 40-2003 and the planned 2008 update: []

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