High power task lighting/ plug lighting

Hi Gahl,
Thanks for your question. This topic is a common source of confusion and varying opinions in the lighting industry. Before I get into discussion about lighting criteria and task-ambient lighting strategies, I want to stress that your design must first of all address the needs of your client. This often means educating your client, and may even benefit from some demonstration or mock-up. Perception of brightness and visual quality is more complex than can be described solely by task-plane illuminance, so to say employees over 60 have an aversion to "the darkness" of 30 fc is likely an over-simplified opinion.

ASHRAE 90.1 - 2007: The LPD for ASHRAE does not include plug-loads. So, officially, plug-in task lights do not need to be included. However, if your lighting design is intented to be a task-ambient system and you are specifying the task lights, it seems to be more in-line with the intent of LEED to include them. There are many very good, low wattage LED and CFL tasklights on the market that will provide plenty of additional light for task specific areas without blowing out your LPD budgets.

Lighting Criteria & the Modern Workplace:
- Traditional Lighting & Criteria: Many clients insist on 50fc avg for their offices. This criteria is based on the IESNA Illuminance Category E, which is based on a task of high contrast and small size. This light level may be appropriate for an employee in their 60's reading black 10-point type on white paper for extended periods of time, or reading blue-line prints.

- Modern Workplace Tasks: Today's workplaces are much more computer task oriented than reading 10-point type or blue-line drawings, so providing 50 fc for the entire office, all day long is not the best use of lighting energy. 30 fc is more than adequate as an ambient base level of illumination for most office tasks today.

Task-Ambient Lighting:
The notion of separating task light and ambient light is to provide an appropriate base illumination level for most tasks (30 fc), then provide individually controlled task lights that can provide 50+ fc for a specific task area for tasks that may require higher light levels. By locating the light source closer to the task area, a higher light level can be provided with much less wattage than could be achieved with the overhead ambient lighting system. The 6W LED tasklight at my desk provides 33 fc on its own, with no ambient light. With 30 fc of ambient light, I have 63 fc availble for specific reading tasks. For only 6W additional in an 80 sqft workstation is only .075 W/SF additional power.

The trick to doing a good task-ambient lighting design is to provide task lights that are low-wattage LED or CFL (6W - 18W) with adjustable position to allow each occupant to adapt the task light to their own preference. Another step is to provide a workstation occupancy sensor to turn off the task lights when the workstation is unoccupied. Additionally, coordinating your design with the furniture layout to provide the 30 fc ambient at the Workstations, and less light for (10fc - 15fc) for Circulation Areas, then you can drive your LPD even lower.

If your client still insists on 50 fc everywhere, you may have a difficult time reducing your LPD to meet your LEED goals.

For more on Low Ambient - Task Lighting, refer to:

http://www.etcc-ca.com/component/content/article/21-Commercial-Office/28...

and

http://www.etcc-ca.com/component/content/article/21-Commercial-Office/28...

I hope this helps,

All the best,
Dane