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Lighting / Electrical Breadth

As a Lighting/Electrical breadth study, an analysis of one lighting space was

performed and the space was redesigned. The space which was selected to be analyzed

and redesigned was the ground floor computer classroom. In this analysis, an alternative

approach to the lighting design of the selected space was performed using a computer

lighting design program called Lightscape. In addition to this rendering of the redesigned

lighting system’s performance, the redesign was assessed in terms of allowable power

density according to the ASHRAE 90.1 standard.

Furniture Layout and Floor Plan of Ground Floor Computer Classroom:

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Existing Lighting Conditions:

The computer classroom on the ground floor has the dimensions, 43’-3”x31’-

2”x8’-0”. The lighting system in this room consists of 4 rows of 20 evenly spaced 2x4

recessed lensed troffers. These 277 V fixtures utilize 3- 32 Watt T8 lamps. They operate

with electronic ballasts and have two different switching zones.

Design Criteria According to the IESNA Lighting Handbook, a space with VDT usage should

have a horizontal illuminance of at least 50 footcandles on the work plane, and a

horizontal illuminance of at least 5 footcandles. The IESNA lighting handbook also

outlines important design considerations for this type of a space. It was considered very

important to control glare in a space like this, as it could detract from the viewing

capabilities of the VDT users in the space. This design consideration has been addressed

in this redesign by changing the existing 2x4 lensed troffers to new Indirect/Direct

pendants. These pendants provide a direct component, but provide most of their

illumination indirectly, thus eliminating much of the glare associated with lighting in

VDT usage. It is also very important to consider the source/task/eye geometry of the

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lighting in this space. This means that it was vital to space fixtures out of an offending

zone for the VDT user so that glare was further eliminated. It was also very important to

keep the illuminances of the room surfaces uniform, therefore eliminating any patterns or

distortions that may be seen in reflections on a VDT screen. This could be done by

spacing the fixtures evenly throughout the space. Daylighting is typically important in

VDT usage spaces, but was not an issue with this space since there are no windows into

the space.

Fixture used in redesign

The classica ID fixture has been selected for this application because it provides

20%-30% downlight for task lighting and the rest as indirect light in order to eliminate

glare in a VDT space. This lamp is four feet long and contains 3 T8 fluorescent lamps, 32

Watts each. It operates at 277 V, and has an electronic ballast.

Light Loss Factors The room cavity ratio was calculated below: RCR= 5h (l+w)/ (l*w) RCR= 5*8’ (43.25’+31.1666’)/ (43.25*31.1666) = 2.199 The maintenance category for the luminaire selected for this redesign was II, the

cleaning interval was assumed to be 12 months, and the space was considered clean.

Therefore, the luminaire dirt depreciation in this case would be (0.94)*(0.068)=0.06392,

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meaning that the expected dirt depreciation was approximately 6.392%. The ballast factor

for this lamp is approximately 0.8. The RSDD for this space is 0.9012. The LLD for this

particular lamp is 2715/2950=0.92. Therefore, the total Light Loss Factor for this fixture

is: 0.7215

Power Density of existing vs Redesign system As it turned out, the power density for both of the designs are the same. Since

both fixtures use the same T8 lamps, and the layouts both have 20 fixtures each, the

power density was: 1720 Watts/2950 ft^2= 1.276 Watts per square foot for each design.

This power density was within the allowable amount for this space as defined in the

ASHRAE standard 90.1.

Performance Results of Redesign system using Lightscape:

Room Layout in Lightscape:

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Rendering from front of room:

Illuminance Values From front of room

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Lightscape Rendering from back of room:

Close-Up renderings of Computer Desk Stations:

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Illuminance Values at Typical Computer Workstations:

Conclusions and Recommendations: The results of the analysis of this redesign showed that the use of these new

fixtures meets all requirements for the illumination and power density of the space. The

use of these fixtures would help eliminate glare from the VDT screens better than the use

of the existing 2x4 troffers in the room. It would therefore be recommended to use this

indirect/direct type of fixture for the lighting design of this space.