SCOTTISH EXECUTIVE

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Building Regulations: Technical Standards

Appendix J: Example lighting calculations

EXAMPLE 1 - LIGHTING CALCULATION PROCEDURE TO SHOW THAT 95% OF LAMPS ARE IN ACCORDANCE WITH THE TABLE TO THE DEEMED-TO-SATISFY SPECIFICATION TO J6.1

A new hall and changing rooms are to be added to an existing community centre. The proposed lighting scheme incorporates lamps that are listed in the deemed-to-satisfy table except for some low voltage tungsten halogen downlighters which are to be installed in the entrance area with local controls. A check therefore must be made to show that the low voltage tungsten halogen lamps comprise less than 5% of the overall installed capacity of the lighting installation.

Main hall

Twenty wall mounted uplighters with 250 W high pressure sodium lamps are to provide general lighting needs. The uplighters are to be mounted 7 m above the floor. On plan, the furthest light is 20.5 m from its switch which is less than three times the height of the light above the floor.

It is also proposed to provide twenty 18 W compact fluorescent lights as an additional system enabling instant background lighting whenever needed.

Changing rooms, corridors and entrance

Ten 58 W, high frequency fluorescent light fittings are to be provided in the changing rooms and controlled by occupancy detectors. Six more 58 W fluorescent light fittings are to be located in the corridors and the entrance areas and switched locally. Additionally, in the entrance area there are to be the six 50 W tungsten halogen downlighters noted above.

Calculation

A schedule of light fittings is prepared as follows:

The percentage of circuit watts consumed by lamps not listed in the deemed-to-satisfy table: formula

Therefore, more than 95% of the installed lighting capacity, in circuit watts, is from light sources listed in the deemed-to-satisfy table. The switching arrangements are in accordance with the deemed-to-satisfy specification for J6.2. The proposed lighting scheme therefore meets the requirements of the Technical Standards.

EXAMPLE 2 - LIGHTING CALCULATION PROCEDURE TO SHOW AVERAGE CIRCUIT EFFICACY IS AT LEAST 50 LUMENS/WATT

A new lighting scheme is proposed for a restaurant comprising a mixture of concealed perimeter lighting using high frequency fluorescent fittings and individual tungsten lamps over tables. Lights in the dining area are to be switched locally from behind the bar. The over-table lamps also have integral switches for diners' use. Lighting to kitchens and toilets is to be switched locally.

The table to this example shows a schedule of the light sources proposed together with a calculation of the overall average circuit efficacy.

From the table, the total lumen output of the installation is 131,800 lumens.

The total circuit Watts of the installation is 2538 Watts.

Therefore, the average circuit efficacy is: formula

The proposed lighting scheme therefore meets the requirements of the Technical Standards.

Note: If 100 W tungsten lamps were to be used over tables instead of the 60 W lamps actually proposed, the average circuit efficacy would drop to 43.4 lumens/W, which is unsatisfactory. If, however, 11 W compact fluorescent lamps, which have the same light output as 60 W tungsten lamps, were used over tables the average circuit efficacy would be 83.2 lumens/W.

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