The LRC has worked extensively on the issues and challenges associated with load management and load-shedding lighting systems.

Human Factors Study: Detection and Acceptance of Dimming
The LRC conducted experiments to understand how well people detect and accept lower light levels. Recent studies by the LRC and others found that people cannot reliably detect light level reductions of up to 20% from the original illuminance level. Furthermore, illuminance levels could be lowered by 30-40% and be accepted by 80% of employees. When workers are educated about the need to reduce electricity consumption and the potential impact at times of peak demand, they accept reduced illuminance levels of up to 50% for short periods of time.

For more information:

• Investigation of Ideal Lamp Light Output Dimming Ratio Required for Different Types of Applications ( 177K)
  Overview of studies and recommendations for dimming needs, lighting system performance and dimming methods
• Energy Savings for Load-shedding Ballast for Fluorescent Lighting Systems
  ( 1284K)
  Discussion of experimental methods and results of a study to identify how people detect and accept illuminance changes
• The Effect of Bias Towards Energy Savings on Occupant's Dimming Requirements ( 1200K)
  Discussion of an experimental study to determine how education plays a role in the acceptance of reduced illumination levels

Load-shed Ballast Prototype
The LRC has developed a low-cost, load-shed ballast prototype for the purpose of reducing lighting loads during times of peak electricity demand.

How It Works
The load-shed ballast is based on an instant-start ballast platform. Added circuitry allows the ballast to receive a signal from an external, central controller and reduce power demand by approximately 33%, lowering light levels 35-40%. Dimming occurs over a period of approximately three seconds so that building occupants do not see an abrupt change.

The central controller that signals the load-shed ballasts is physically located within the facility and can be controlled locally by the facility manager or remotely by a utility or transmission system operator. The controller sends the signal to the individual ballasts via a power line carrier. Because the ballast requires only a simple on-off signal, minimal bandwidth is sufficient. This low bandwidth power line carrier is made robust and reliable by employing sub-60 Hz modulation and long signal integration times. This solution has the added advantage of not requiring additional wiring, making it cost-effective.

Dimming Issues
For operating lamps without additional electrode heating, LRC study results show that a T8 fluorescent lamp dimmed to about one-third of nominal operating current (as in the case of the load-shed ballast) keeps a reasonably long life. Dimming 100 hours per year at 67% of rated current levels is expected to reduce overall life by less than 20% (20,000-hour rated life reduced to 16,000 rated hours).

Economics
The load-shed ballast system's incremental cost is approximately $9 per ballast, compared with an incremental cost of $35 for a full dimming ballast.

For more information:

• Revised Draft Performance Specification: Load-shed Ballasts ( 139K)
  Recommended operational specifications for a prototype load-shed ballast
• Market Analysis for Load-shedding Ballasts ( 213K)
  Analysis of customer savings/payments and ballast and communication link costs