Lighting for Interior Design

Posted: August 27th, 2021

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ASSIGNMENT 7 – Lighting for Interior Design

            The purpose of the paper is to calculate the average maintained illuminance on a work surface in a library’s study room. Space has the following characteristics:

1. Dimensions: 60 feet by 60 feet with a 12-foot ceiling
2. Work surfaces: 2 feet 6 inches (AFF)
3. Distance from luminaires to work surfaces: 5 feet 6 inches
4. Reflections in space: 70 percent ceiling, 50 percent walls, and 20 percent floor.
5. Clean space with lamp cleaning three times a year
6. 24 surface-mount luminaires (fig. 8.4) with two F32 T8 lamps in each luminaire. Initial lamp lumens: 2800
7. LLD –
8. LDD –

            The following formula will be used in determining the average maintained illuminance on the work surfaces in the library:

Given that there two F32 T8 lamps in each luminaire with 24 surface-mount luminaires, the number of lamps will be;

Light loss factor (LLF) shows the illuminance lost due to the type of lamp, the temperature of the space, time, input voltage, ballast, lamp position, and interior conditions, among others. It is calculated as follows;

Whereby;

LLD is the Lamp Lumen Depreciation, in this case with a factor .93 for T8/830 Lamps while LLD accounts loss of light due to dirt and dust is equivalent to 1 – 0.7= 0.3

Hence, LLF = 0.93 * 0.3 = 0.279. Finally, the coefficient of utilization (CU), which relies on the space to be illuminated and the design of the luminaires, is obtained using the Room Cavity Ratio (RCR) calculated as follows;

H is the room’s height or the distance from the luminaire, L is the length of the room, and W is the room’s width. In this case;

For an RCR of 2 with typical lamp distribution and percent lamp lumen of 70 percent ceiling, 50 percent walls, and 20 percent floor reflections, CU is equivalent to 0.47. Since the space area is 60 * 60 = 3600 square feet;

Therefore,

=