Field Test Results

The lights were automatically turned on at 6:30 am and turned off at 7:00 pm in order to mimic the normal operation of the lights in that building. On a sunny day, the east facing windows of the office provided an abundance of natural sunlight that could be harvested.

The blue curve in Figure 1 shows the relative light level, at desk height, that was measured in the room. The 100% level on the Y-axis represents the desired light level set point that would be produced at desk height if the fluorescent lamps are fully on and there is no natural light (ie: blinds closed in the evening). As the sun comes up in the morning of a sunny day, there is an immediate source of natural light. The automatic controller for the fluorescent lamps detects the excess light in the room and dims the fluorescent lamps accordingly to maintain the 100% desired light level. By 7:30 am, the fluorescent lamps are dimmed to their maximum level, which is 32% for this installation. There is still excess light which could not be harvested since the lamps were not allowed to dim any further. The red curve in Figure 1 shows the power consumption of the fluorescent lamps relative to their 100% full brightness power consumption over the course of the day.

Figures 2 and 3 show the effects of a non-ideal day on the light harvesting capability of the fluorescent dimming system. On a cloudy day in Figure 2, the maximum dimming level was reached for only a short time twice during the day. However, sustained dimming at 65% did occur in the afternoon offering significant energy savings.

Figure 3 is representative of a worst case scenario where the entire day was overcast, gloomy, and rainy. Once again, it was possible to harvest light continuously in the afternoon.

The data collected over more than 5 months of testing in the Hamilton office tower installation showed that an average power consumption reduction of approximately 40% could be achieved using the dimming fluorescent ballasts in a light harvesting scheme. The field test operated only 12.5 hours per day so as to simulate the normal operation of the lights in that building. Many buildings are left with their fluorescent lamps on at night. The Dim&Save system would automatically dim to the minimum power consumption level at that time. Hence, additional savings could be achieved for offices illuminated in that manner. The possible energy savings can be analyzed according to the two cases:

1) Lights operated 12.5 hours per day

An average 40% consumption reduction translates into an energy saving of 2.3 kW-h over the course of the 12.5 hour day. At an electricity cost of $0.085 per kW-h, this energy saving will reduce the hydro costs for that particular room by approximately $5.86 per month.

2) Lights operated 24 hours per day