Light level for a workplace is a significant factor for productivity and mood of staff. Poor lighting (as a result of light flickering, strong glare, excessive contrast, uneven distribution or under supply) can lead to problems like occupational accidents, headaches and eye illnesses. Proper lighting, on the other hand, reduces electricity cost, reduces risk of occupational accidents, creates aesthetics and improves concentration and accuracy in work.
It is therefore important that you understand the adequacy and quality of light for your office. The quality of light (or illuminance) is measured by a luxmeter and the measured illuminance is displayed in lux (lx).
Light quality is an occupational health and safety issue, thus, must be taken seriously. A system of lux measurement called light ergonomics can be used to define appropriate lux for a workplace. It is recommended that a work station (e.g. desk area) should have between 300 to 500 lux and 1200 to 1600 mm above floor level should be lit to 150 lux. Further recommendations on the lighting level are as shown in the table below.
Recommended Illumination for Workplaces
|Activity||Light Level (Lux)|
|Performance of very special visual tasks of extremely low contrast and small size||10000 – 20000|
|Performance of very prolonged and exacting visual tasks||5000 – 10000|
|Performance of visual tasks of low contrast and very small size for prolonged periods of time||2000 – 5000|
|Detailed Drawing Work, Very Detailed Mechanical Works||1500 – 2000|
|Normal Drawing Work, Detailed Mechanical Workshops, Operation Theatres||1000|
|Supermarkets, Mechanical Workshops, Office Landscapes||750|
|Normal Office Work, PC Work, Study Library, Groceries, Show Rooms, Laboratories||500|
|Easy Office Work, Classes||250|
|Warehouses, Homes, Theaters, Archives||150|
|Working areas where visual tasks are only occasionally performed||100 – 150|
|Simple orientation for short visits||50 – 100|
|Public areas with dark surroundings||20 – 50|
|Normal Work Stations||300 – 500|
|Conference Room, Executive Offices||500|
|Computer and Data Preparation Rooms||500|
|Auditoria||150 – 200|
|Banks and Other Financial Institutions|
|Counter, Office Area||500|
|Reception, Cashiers and Prospers’ Desks||300|
|Bars, Coffee Lounge, Dining Rooms, Restaurants Lounge||50 – 200|
|Cloakrooms, Baggage Rooms||100|
|Bathrooms||50 – 100|
|Small Retail Outlets||500|
|Grocery, Vegetable Stores||1000|
|Showrooms||500 – 700|
|Covered Arcades and Malis||50 – 300|
|Entrance Lobbies, Atria||200|
|Elevator Lobbies, Public Corridors||200|
|Ped. Tunnels and Bridges||200|
|Staff Locker Rooms||200|
|Storage Rooms, Janitors’ Closets||200|
|Electrical Rooms, Generator Rooms||200|
|Dining Areas 150-200 Kitchens 500 Outleased Space 500 Physical Fitness Space 500 Child Care Centers 500 Structured Parking, General Space 50 Structured Parking, Intersections 100 Structured Parking, Entrances 500|
|Dining Areas||150 – 200|
|Physical Fitness Space||500|
|Child Care Centres||500|
|Structured Parking, General Space||50|
|Structure Parking, Intersections||100|
|Structure Parking, Entrances||500|
Illuminance is achieved by the number, spacing, positioning and design of lighting points. Many light fixtures are designed to reflect light off walls, ceilings and objects. Illuminance is also determined by the colour temperature. For example, warmer colours (e.g. warm white) tend to create more relaxed environment while cool white keeps staff alert. Poor of insufficient lighting can be corrected by:
- Replacing bulbs on a regular schedule. Old bulbs give less light than new ones, so replace them before they burn out. Follow manufacturers’ instructions.
- Clean light fixtures regularly. Dirt on light fixtures reduces the amount of light given off. Light fixtures with open tops allow air currents to move dust up through the fixtures so dust and dirt do not accumulate on them.
- Add more light fixtures in appropriate places.
- Paint walls and ceilings light colours so light can be reflected.
- Use more reflected light and local lighting to eliminate shadows. For example, a covered light mounted under a transparent guard on a grinding wheel provides the added light needed to clearly see the task.
- Do not position work station with light fixture directly behind a worker.
Determination of Illumination
To determine illumination of your workplace, you can use the following formula.
- Given that Lux = Lumens (quantity of light) per square metre;
I = Ll X Cu X Llf/Al
I = Illumination (lux, lumen/m2)
Ll = Lumens per lamp (lumen)
Cu = Coefficient of utilization
Llf = Light loss factor
Al = Area per lamp (m2)
5 incandescent lamps of 20 W (10600 lumens per lamp) are used in an area of 40 m2. With Cu = 0.6 and Llf = 0.8 illumination can be calculated as:
I = 5 (10600 lumens) x (0.6) x (0.8) / (40 m2)
Illumination = 636 lux
You can also work backwards to determine the number of light points, given amount of illumination and workplace area.
How to Make a Choice
Lumens are a better measurement to purchase light fixtures as compared to watts. One should therefore consider lumens to watts when deciding on light fixtures to purchase. For instance, an LED bulb can produce as many as 60 – 100 lumens per watt as compared to an incandescent bulb that only produces 12 – 17 watts. For purposes of conversion, please note that:
This implies that to replace a 40W standard bulb in your workplace, you need a bulb that gives 450 lumens. Comparatively, LED and CFL bulbs have less wattage but still produce more.
Contact us for on illumination assessment and correction for your workplace illumination:
|info(at)deprissgrp.co.ke | +254 739 669 914 | @depriss1