One example of task ambient lighting is for a 20 foot x 40 foot room where the primary tasks are drafting and design of printed circuit boards. The drafting and design area is located in the center of the room, occupying about a quarter of the available space. Recommended levels of illumination are 1,000¡V2,000 lux. The staff in this area requested that the higher levels of illumination be provided as there have been reports of difficulty in performing some required visual tasks.

Standard design practice would be to design the entire room to the 2,000 lux level, which would require 32 2x4 troffers with four 32WT8 lamps in each fixture. This standard design assumes reflectance of 80 percent ceiling, 50 percent walls, and 30 percent floors. This standard layout will provide the required 2,000 lux; the luminance range will average 2,090 lux and have a minimum level of approximately 920 lux.

The energy density of the space would be 4.4 watts/sqft.

Calculation:
32WT8 with 4-light electronic ballast (including ballast loss)	27.5 watts
32 troffers with 4 lamps each	128 lamps
128 lamps x 27.5 watts	3,520 watts
Room size 20 x 40	800 sqft
Energy density (3,520 watts/800 sqft)	4.4 watts/sqft

If a lighting designer decided to use the ambient task lighting approach discussed above, the layout would be much different. Placing six 4 ft x 4 ft troffers, each with eight 32WT8 lamps, over the center area of the lab would provide the luminance desired for the drafting and circuit design tasks being performed. There would be an average of 2,050 lux delivered to the work surface over the task area, meeting the needs of the space. The light levels would drop off in the general areas to an average of about 300 lux, which will be more than enough light for the occupants to navigate through the space.

Calculation:
32WT8 with 4-light electronic ballast (including ballast loss)	27.5 watts
Six troffers with 8 lamps each	48 lamps
48 lamps x 27.5 watts	1,320 watts
Room size 20 x 40	800 sqft
Energy density (1320 watts/800sqft)	1.65 watts/sqft