Lighting Design Requirements in Process Industry

This article is for general plant lighting design, emergency lighting, safety lights, and aircraft obstruction lighting technical requirements and specification required in plants, refineries and process industries. Lighting design requirements in plants and refineries are crucial for ensuring safe and efficient operations in these industrial environments.

References

American Petroleum Institute (API)

RP 540 Electrical Installations In Petroleum Processing Plants.
Federal Aviation Administration – Advisory Circular (FAA).
AC 70/7460 Description of FAA Standards for Marking and Lighting Structures to Promote Aviation Safety.

Illuminating Engineering Society of North America (IESNA) Lighting Handbook
RP 7 Recommended Practice for Industrial Lighting.

National Fire Protection Association (NFPA)

NFPA 70 National Electrical Code.
NFPA 101 Life Safety Code.
Code of Federal Regulations, U.S.A.
Title 14, Chapter 1, Part 77 Objects Affecting Navigable Airspace.

Definitions

For the purpose of understanding this standard the following definitions apply.

Candela. SI unit of luminous intensity. One candela = one lumen per steradian (candle power).
Illuminance. The density of luminous flux incident on the surface. The quotient of the total luminous flux by the area to be lighted assuming the area is uniformly illuminated. [Footcandles or Lux (1 FC = 10.76 Lux)].
Initial LX. Average illuminance level in Lux when luminaires are clean, and when the lamps are first energized.
In-Service LX. Average illumination level in Lux over an extended period.
Lumen. SI unit of luminous flux. The time rate of the flow of light.
Luminaire. A complete lighting unit consisting of lamp(s) together with parts designed to distribute the light.
Reflectance. The ratio of reflected luminous flux from a surface to incident flux.

Lux Lighting Levels

The values shown in Table I are minimum average maintained illuminance requirements. The installation shall be designed for the conditions of the specific task; greater levels of illuminance may be required in some cases. Table values meet or exceed API 540 and IESNA RP 7 recommended lighting levels.
The illumination levels are average vertical component values for a horizontal plane 76 cm above the floor, ground or platform.

Lighting Design Calculations

General

Software can be used for lighting calculations.
There are two methods of performing lighting calculations: the Lumen Method and the Point-by-Point Method. For more detailed information on these calculations see the IESNA Lighting Handbook.

Lumen Method for Lighting Design

The Lumen method is the most frequently used technique to determine Iighting levels, and provides the average maintained level of illumination on a horizontal plane, usually designated as the work plane. This method is applicable to systems using any type of light source. The Lumen method is usually used for indoor lighting where uniformly distributed light is required over a large area.
In a lighting system, all lumens produced by the lamps do not reach the work plane due to losses in the luminaire and the absorption of light by the room surfaces. These losses are accounted for by the application of the coefficient of utilization for the luminaire being used.
The usual criteria is to design the lighting system to maintain a minimum level of illumination throughout its life. The light output of the lamps depreciates during service, so the initial light level of the system shall be increased to account for these losses. Causes of depreciation are:
a. Loss of lumens as a result of aging
b. Decrease in lamp and luminaire output resulting from dust, dirt, insects and chemical changes in reflecting surface
c. Increased absorption of the light by dust, dirt and changes in the rooms reflecting surfaces
d. Differences between actual and design lamp voltages
The mathematical equation for the Lumen Method is as follows:
a. LUX = {LL x N x CU x LLD x LDD} divided by A
Where:
LL = Initial lamp lumens per luminaire
N = Number of luminaires (fixtures)
CU = Coefficient of utilization
LLD = Lamp lumen depreciation
LDD = Luminaire dirt depreciation
A = Area in square meters
b. In most lighting design, the required maintained Lux intensity will be a known quantity. It will be either given in basic data or selected from standard tables. Therefore, by transposing the terms in equation above, the required number of luminiaries can be computed.
N = {LUX x A} divided by {LL x CU x LLD x LDD}
Table I can be used to determine the required lighting level. In some cases, the recommended illumination levels are given for specific tasks, and apply only to the area where the task is to be accomplished. In these cases, the general area around the task should have one-third to one-fifth the illumination required for the task. This technique is known as task-ambient or nonuniform lighting.
Location of the fixtures shall then be determined.
a. Perfect uniformity of illumination is usually not feasible. Some deviation from the average is to be expected. Illumination nonuniformity shall be considered acceptable if the maximum and minimum values in the area (except for extremities, for example corners) do not exceed 10 percent above or below the calculated average. b. To achieve acceptable uniformity, the luminaire spacing to mounting height ratio, from vendor’s data (catalogs), should not be exceeded. The commonly used practice of letting the distance from the luminaires to the walls equal one-half the distance between rows often results in inadequate illumination near the walls. In areas where desks or work benches are located along the walls, a distance of 760 mm from the wall to the center of the luminaire should be used to avoid excessive drop-off in illumination. This will locate the luminaires over the edge of the desks facing the walls or over the center of the desks that are perpendicular to the walls. In critical areas, for example drafting rooms, where tables are located against the walls, it is often desirable to use somewhat closer spacing between luminaires adjacent to the walls.
c. To prevent excessive reduction in illumination, the ends of fluorescent luminaires should not be located more than 610 mm from the wall. Often, increasing the number of lamps in the end units will satisfactorily prevent drop-off in intensity at the ends of a room.
d. Spacing closer than the maximum permissible is often highly desirable to reduce harsh shadows and ceiling reflections. This will also improve uniformity, particularly when using direct and indirect type of luminaires.

Point-by-Point Method for Lighting Calculation

Point-by-point calculations provide horizontal or vertical levels of illumination at a point and do not take into account inter-reflections or depreciation of system components. Its application is limited to essentially point light sources, for example incandescent and high intensity discharge (HID). Point-by-point calculations for linear sources (fluorescent) are quite complex and normally require the use of a computer. The point-by-point method is normally used for outdoor lighting to ensure minimum illumination along the boundary of the area, or indoors for checking the illumination on vertical surfaces, for example control panels.
The point-by-point method provides a means of determining the level of illumination on any point in a given area. It is especially useful for calculating illumination on vertical or oblique surfaces.
In theory, the source of light is considered to be a point. In practice, computations will be accurate when the distance from the source to the point in question is at least five times the maximum dimension of the source. Luminaires which meet this dimensional restriction can be considered as point sources in this method of calculation.
The laws of photometry related to the point-by-point calculations are the inverse square law and Lambert’s cosine law. The intensity of illumination at a point on a surface is inversely proportional to the square of the distance from the source to the point and directly proportional to the candela of the source in the given direction.
Two basic formula are generally used for point to point calculations:
a. For horizontal surfaces:
Lux = {Candela x cos(a)} divided by D2
b. For vertical surfaces:
Lux = {Candela x sin(a)} divided by D2
c. The fixture light output in candela (in the direction of the point to be calculated) is obtained from the manufacturer’s catalogue. The angle ‘a’ is the angle between a line through the point and perpendicular to the plane on which the point lies and a second line between the point and the light source. ‘D’ is the distance in meters from the light source to the point.
d. A separate calculation has to be made for each fixture near the point in question. The results are added together to arrive at the total illumination at that point. For example, a point at the side of a relatively narrow pipe rack would receive significant light contributions from at least three fixtures. A calculation would be made for the contribution of each fixture.

Lighting Coefficient of Utilization

The coefficient of utilization (CU) is used to perform calculations using the Lumen Method. It is the ratio of the light output in lumens reaching the work plane, to the total lumens generated by the lamp. It takes into consideration the efficiency and distribution of the luminaire, its mounting height, the room proportions, and the reflectance of the walls, ceilings, and floor. The zonal cavity method is used for calculating the coefficient of utilization.
The selection of a coefficient of utilization by the zonal cavity method is a four step computation:

a. Determine the cavity ratios
b. Determine effective ceiling and floor cavity reflectance
c. Select coefficient of utilization
d. Correct the coefficient of utilization selected for effective floor cavity reflectances other than 20 percent

To determine the cavity ratios, the room or area has to be divided into cavities. These cavities are dependent upon the luminaire mounting height and the location of the work plane. See IESNA Lighting Handbook for calculation of cavity ratios.
Effective cavity reflectance shall be determined for the ceiling cavity and for the floor cavity respectively. These can be selected from charts in IESNA Lighting Handbook under the particular combination of cavity ratio and in-service reflectance of the ceiling, walls, and floor.
White has a reflectance value of approximately 80 percent, light blue and ivory 70 percent, beige and aqua green 60 percent, light gray and rose 40 percent, and dark brown, gray, and green around 15 percent. The actual reflectance should be determined from the selected finishes and should be averaged in accordance with area covered when several finishes are present.
Using the values of effective ceiling cavity reflectance, the percentage wall reflectance, and the room cavity ratio, the coefficient of utilization should be selected from the manufacturers’ data for the fixture under consideration.

Lighting Depreciation Factors

The depreciation factor accounts for the loss of illuminance from a lighting system after a given period of time and under given conditions. It takes into account temperature and voltage variations, dirt accumulation on luminaire and room surfaces, lamp depreciation, maintenance procedures, and atmospheric conditions.
The objective in lighting design calculations is to predetermine maintained illuminance. Factors have to be included in the equation to account for depreciation of all elements within the space and lighting system that normally occur over a period of time.

Glare Reduction Requirements

A lighting system is often judged by the level of illumination provided. Attaining a recommended light level will not always ensure adequate visibility. Good quality light is also important for adequate visibility, and is usually more difficult to achieve. The common causes of visual disability and discomfort are glare and excessive brightness ratios. Glare is defined as any annoying brightness in the field of view. Glare conditions may be either direct or reflected:
a. Direct glare (often called discomfort glare) results when inadequately shielded light sources, overly bright luminaires, or large bright areas occupy a significant portion of the field of view
b. Reflected glare results when the bright surfaces of luminaires or large areas reflect from the specular (reflective) surfaces on, for example machines and furniture. When the specular surface is part of the seeing task, a veiling effect will obscure the task. If the specular surface is adjacent to the seeing tasks, the reflection will continually attract the observer’s attention towards the annoyance.
IESNA Lighting Handbook describes a system for classifying the visual comfort probability (VCP) of lighting systems. This system permits the calculation of discomfort glare ratings of luminaires, taking into consideration all the pertinent characteristics of the light system. The system and calculation procedure is applicable to the preparation of:
a. General glare tables for typical types of luminaires
b. Tables for specific luminaires
c. Ratings of specific lighting layouts
Methods for reducing reflected glare are:
a. Do not cover desk and tables with specular surface glass or plastic. Use dull or mat surfaces to reduce the primary cause of veiling reflections.
b. Orient the task or the luminaires to avoid the latter being readily reflected
c. Install lighting systems that have lower brightness in the reflected glare zone. Fluorescent luminaires should be used in preference to incandescent or mercury in open-bottom units. Luminaires with bottom diffusing panels, or luminaires with semidirect distributions, will reduce reflected glare conditions.
d. Parabolic lighting covers can be used with most standard fluorescent fixtures, to significantly reduce glare on computer video monitors

Office Lighting Design

Office lighting installations should provide an efficient and comfortable environment to maximize productivity. Office tasks include viewing material with poor contrast at close range; also, tasks include viewing data displayed on a cathode ray tube. Care should be exercised in the selection of light sources, luminaires, and room surface reflectances. Maintenance requirements and economics are other parameters to consider in selecting an acceptable design.
Standardized tables have been prepared which can be used in lieu of detailed calculations for office lighting. These tables are available from manufacturers for various fixture types. To utilize the tables, the designer should select an arrangement compatible with the required intensity of illumination. It is not necessary that actual room dimensions match those shown in the table. Selection of the room dimension most nearly matching the area in question will be acceptable in the majority of installations, as the variation in intensity will be negligible.
Economics shall be considered in the design of a lighting system. In general, the use of the least number of luminaries which meets the spacing-to-mounting height ratio for the luminaire will provide the most economical installation. In office lighting design, the 61 x 122 mm luminaire usually proves most economical.

Control Room Lighting

Lighting for control rooms, panels and consoles presents many seeing tasks and conditions not typical of work areas in general. More emphasis is placed on vertical plane illumination than is usually encountered in the design of interior lighting.
Computer monitors have become the predominant means of displaying information in the control room. Special lighting treatment is required to provide good visibility for display screens, and to maintain adequate lighting on board mounted instruments and graphic displays.
Lighting shall be designed to illuminate vertical board mounted equipment, DCS operator console monitors and details without glare. Control room lighting shall be a combination of indirect and direct lighting.
All light fixtures in control room shall be provided with flicker-free dimmer control. Fixtures shall be controlled in sensible groups to provide optimum lighting.
Diffused lighting can be provided by means of wall-to-wall (or a large portion thereof), louvered, or translucent plastic luminous ceilings. Luminous ceilings have three interrelated functional elements; a plenum cavity, a light source, and a diffuser. The plenum cavity contains the lamps, and the cavity surfaces serve as the light reflector. The diffuser is made up of suitable plastic (acrylic) sheets resting freely on a supporting framework. A uniform ceiling brightness in all directions is obtained by proper lamp placement, diffuser translucency, and diffuser patterns. The distance between continuous rows of lamps should not be greater than twice the height of the lamp above the diffuser panels. For proper translucency, the plastic panels should have incident transmittance limits between 45 and 55 percent. A uniform surface viewing angle from all directions may be obtained with dimpled-pattern panels. Cavity surfaces should be finished with a paint having a diffuse reflectance of 85 percent or more.
Directional light can be provided by means of troffer units (equipped with parabolic louvers) set flush in the ceiling (or suspension mounted), or by units especially designed to provide lighting on vertical surfaces. Such units generally are installed in rows following the contour of the panels. In this method, the luminaries shall be accurately located, to keep reflections away from viewer’s glare angle and to minimize shadows cast on the instrument scales due to their case overhang. The use of directional light with control systems using CRT displays reduces flexibility of the space. More detailed planning of the space and lighting system is required to ensure their proper physical relationship to each other.

Process Area Lighting

Piperacks

All onsite piperacks shall be illuminated using pendant mounted HPS fixtures mounted from the rack steel or bracket mounted fixtures, or both, attached to rack columns.
Fixtures installed under the main piperacks shall have the lowest part a minimum of 3.7 m above grade.

Equipment adjacent to piperacks shall be illuminated by floodlights mounted on the upper elevation of the piperack whenever possible.

Structures, Equipment Bays, Ladders and Platforms

In general, fixtures should be mounted 3 m or more above the finished floor or grade. In locations where head room is limited, the mounting height can be reduced to 2.4 m.
Platforms and ladders shall usually be illuminated with stanchion mounted HPS fixtures on masts attached to the handrails. These fixtures shall have reflectors, globes and guards.
Fixtures shall not be mounted directly over equipment having exposed movable parts or equipment emitting appreciable heat or fumes. Care shall be taken in placement of fixtures to avoid interference with maintenance activities and yet provide adequate lighting for routine operations.
In placement of fixtures consideration shall be given to maintenance of the lighting system. Fixtures installed on tower platforms and similar locations shall be accessible from the platforms or from structural ladders.

Area Floodlighting and Building Exterior Lighting

Flood lighting shall be used to the maximum extent possible for illumination in the process areas. Flood lighting fixtures shall be mounted high enough and aimed so as not to be objectionable or blinding to personnel.
Surface temperatures of floodlight fixtures shall meet the area classification requirements. These fixtures usually have larger lamps and operate at higher temperatures. It is frequently necessary to place them outside of the classified area, and this can sometimes be accomplished by the use of taller floodlight poles.
Bracket mounted fixtures or floodlights shall be used to illuminate the entrances to buildings. Special care is required to avoid blinding of persons approaching the buildings.
When practical, floodlights can be installed on the exterior of buildings, to provide area floodlighting. Care shall be taken to avoid excessive glare and blinding.
When poles are used for mounting floodlights they shall be spun aluminum. Aluminum poles installed in corrosive areas shall be painted or otherwise coated for corrosion protection.
Maintenance of floodlights requires provisions for access. If the structures or poles can be reached by aerial lift trucks the problem is simplified. Otherwise, provisions shall be made for lowering the fixtures to the ground (hinged pole) or other arrangement made to reach the fixtures.

Emergency Lighting

Facilities shall have an emergency or standby power system. This system shall provide power for an orderly plant shutdown and emergency lighting.
In occupied buildings, sufficient lighting fixtures shall be supplied from emergency lighting to maintain a minimum of 11 lux during outage of utility power. Buildings in this category shall include offices, laboratories, shops and occupied areas of warehouses.
Control rooms, electrical substations, electrical equipment rooms and operation/maintenance emergency command centers shall have 100 percent of lighting fixtures supplied from emergency power.
Approximately 20 percent of the fixtures in active operating areas shall be on emergency power, to provide safe access and egress for workers. Additional fixtures in utility areas shall be placed on emergency power as necessary to facilitate maintenance of critical utilities and restoration of all utilities to the facility.
Security and safety lighting shall be supplied from emergency power in accordance with the applicable Security and Safety Directives.
All HPS fixtures supplied from emergency power shall have instant restart (hot restrike) ballasts.
Exit lights shall be installed within buildings to identify route out of area, and shall be a battery pack type fixture.
Emergency lighting shall comply with NFPA 101.

Obstruction Lighting

The purpose of marking and lighting an obstruction that presents a hazard to air commerce is to warn airmen of the presence of such obstructions.
Title 14, Chapter 1, Code of Federal Regulations, U.S.A., Part 77 shall be used as a guide for identifying obstructions that require marking or lighting requirements. It shall be modified as necessary to meet any requirements of the local authority. In most cases notice has to be filed with the local authority of the intention to build.
FAA Advisory circular 70/7460, published by the Director of Air Traffic Rules and Procedures Services, describes the FAA standards for marking and lighting structures to promote aviation safety. This document shall be used as a guide for making and lighting structures, and shall be modified as necessary to meet any requirements of the local authority.
Generally, objects, structures, or portions thereof, that are of sufficient overall height as to present a hazard to air navigation, usually 45.7 m or more, and situated within limits of proximity to airports or airways, are subject to obstruction marking requirements.
Where the structure will be shielded by other structures which are equal to or greater in height, marking shall not usually be required.
Safe access to obstruction lighting fixtures installed on stacks and similar structures is a major consideration. The costs and physical hazards in the continuing maintenance of fixed-position obstruction-light fixtures at some locations may justify the increased costs of disconnecting- and lowering-type hangers.
Disconnecting-type hangers and accessories are available for duplex obstruction lights and beacons meeting the installation conditions for mounting heights up to 137.2 m.
Depending upon energy and maintenance costs, it may be more economical to provide stack and similar obstructing lighting by fixed-position floodlights instead of by obstruction lights and flashing beacons previously described. Such floodlights shall be installed at three or more points of approximately equal distances around the obstruction in a horizontal plane.

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