What is a Lumen?


What is a Lumen?

The quantity of light reaching a surface is usually the main consideration in designing a lighting system.

This quantity of light is specified by illuminance measured in lux, and as this level varies across the work surface ‘working plane’, an average figure [lumen] is used.

CIBSE Lighting Guides give values of illuminance that are suitable for various areas.

Location

Illuminance (lux)

Limiting Glare rating

Minimum colour rendering (Ra)

Restaurant, function room.

80

Auditoria

100

General lighting healthcare

100

19

80

Toilets domestic

100

80

Lounge domestic

100   – 300

19

80

Kitchens domestic

150   – 300

80

Bathrooms domestic

150

80

Archives store   office

200

25

80

Foyers

200

Self service   restaurant

200

22

80

Classrooms

300

19

80

Computer practice   rooms

300

19

80

Filing, copying etc.

300

19

80

Practice rooms,   dressing rooms

300

22

80

Reading lighting   healthcare

300

19

80

Reception desk

300

22

80

Sales area

300

22

80

Simple examinations

300

19

80

CAD work stations

500

19

80

Conference and   meeting rooms

500

19

80

Conference rooms

500

19

80

General office   lighting

500

19

80

Kitchen

500

22

80

Till area

500

19

80

Wrapper table

500

19

80

Technical drawing

750

16

80

Technical drawing   room

750

16

80

Examination and   treatment

1000

19

80

Lighting Levels are detailed  in the table below. Illuminance values are shown in Lux, together with typical locations.

Illuminance (lux)

Activity

Area

100

Casual seeing

Corridors, changing rooms, stores

150

Some perception of detail

Loading bays, switch rooms, plant rooms

200

Continuously occupied

Foyers, entrance halls, dining rooms

300

Visual tasks moderately easy

Libraries, sports halls, lecture theatres.

500

Visual tasks moderately difficult

General offices, kitchens, laboratories, retail   shops.

750

Visual tasks difficult

Drawing offices, meat inspection, chain stores.

1000

Visual tasks very difficult

General inspection work.

1500

Visual tasks extremely difficult

Fine work and inspection, precision assembly.

2000

Visual tasks exceptionally difficult

Assembly of minute items, finished fabric   inspection.

The lumen method is used to determine the number of lamps that should be installed for a given area or room.

Calculating for the Lumen Method

The lumen method is used if the light fittings (luminaires) are to be mounted in a regular pattern.

The luminous flux output (lumens) of each lamp needs to be known as well as details of the luminaires and the room surfaces [colours and textures of surface finishes].

Usually the illuminanceis already specified e.g. kitchen 300 lux,  office 500 lux etc.

The number of lamps is given by the formula:

where,

N    =              number of lamps required.

E    =              illuminance level required (lux)

A    =              area at working plane height (m2)

F    =              average luminous flux from each lamp (lm)

UF=               utilisation factor, an allowance for the light distribution of the luminaire and the room surfaces.

MF=              maintenance factor, an allowance for reduced light output because of deterioration and dirt.

Example

A production area in a factory measures 24 metres x 60 metres.

Find the number of lamps required if each lamp has a Lighting Design Lumen (LDL) output of 18,000 lumens.

The illumination required for the factory area is 200 lux.

Utilisation factor = 0.4

Lamp Maintenance Factor = 0.75

N             =              ( 200 lux x 24m x 60m ) / ( 18,000 lumens x 0.4 x 0.75 )

N             =              53.33

N             =              54 lamps.

Correct lighting design can have a huge effect on how a space is illuminated and the ambiance created. We can work with you by first taking accurate lux readings of your present installation. We will then identify what light levels you want and see what can be done to cost effectively meet your requirements.

Contact us on 01782504503 or 07901380746 to  discuss your requirements. You can also e-mail ecologic@gmx.co.uk to arrange a meeting or ask any questions you may have about lighting and general energy efficiency issues.

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About aimhome
All aspects of energy efficiency and help with saving money spent on utility bills. Home visits undertaken to assess what is used and explain what can be done to save money. Central heating control upgrades, central heating system power flushing. Energy saving lighting surveys and installation of low energy lamps and lighting. Every day that action is not taken is an added cost in hard cash terms. Call today to see what can be done. Green Deal Ecologic Ltd, improving your world without costing the earth.

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