PIR . Passive Infra Red. Motion detector simular to an alarm motion sensor, they work off of senseing heat moving from one lensed or mirrored zone to another. So they will pick up just about any thing that presents a tempurature diffrence, people, cars, pets, mice, birds, shopping carts, air ducts, high wattage lighting, green laser pointers ( over 50 mW work the best even threw the store windows at 1000 feet )
But if your looking to dim the lighting while the malls closed use dimmable ballasts on a timer, and If I was you look at the most common type fixture you use in the mall or parking lot areas, as some ballasts can be "Converted" by simply adding a dual capacitor to them, also look at dimming parking area if say you have a open air multi story parkade, during the day, so long as lights are on it's usally not a big issue and turn them up at dusk till dawn or closing time which ever you like.
And some thing to remember if your going dimmable, when they are first powered up allow them to run at full 100% brightness for 15 mins then you dim them, and you'll find some lamps may not last as long while dimmed. but the 40% power savings soon outway the few hundred hours diffrence the light will last. ( but HPS lamps can get very ugly CRI results when dimmed, but if you only need it for security reasons it's not a issue for any electronic camera ) infact they work better in the red end of the spectrum )
Who's ballasts are they using in the street lighting ? just wondering because I was doing some work at a parking lot useing Lithonia's metal halide fixtures, controled with there more then fun synergy controller and dual level 100% / 50% pulse start 175 watt metal halide ballasts and over 40% of the fixtures look as though they have suffered from some sort of fire inside the fixture distroying the ballasts. ( for Lithonia eye's CPSC is getting a notice of this )
So I'am more or less looking for a reliable ballast for this application ( Personally I'd just goto a 70 HPS and chalk it upto a 100 watt saving per fixture but that's to simple for the owner...something about a allergy to orange light ?? )
To answer your question correctlly. Installating dimmable ballasts do save on energy on dimming mode.But there are issues to be addressed in this context. It is very effective when it is used in co juction with day light harvesting other wise just installing dimmable ballasts and a suitable dimming panel will only increase the cost of installation and not give the desired benefits. The alternative system of energy saving is based on bucking and boosting of voltage in case of large installation ;but then these are useful and have proved sucessful in case of streetlighting installations only.
The answer to your question is yes, you can save energy using dimming ballasts. The way to do it can be:
1. Manual control: Using a 1-10V dimmer for 1-10V ballasts or DALI dimmer for DALI ballasts.
2. Daylight-dependent dimming: Using a light-sensor either 1-10V or DALI depending on the specified ballasts. The light-sensor can be set to a particular lux level and if any additional daylight bumps up this value, the light-sensor will command the ballast to dim the lights down thereby saving you energy.
You donot need dimming ballasts to save energy if PIRs are used as switching is independent of dimming for analogue 1-10V dimming ballasts and using DALI ballasts just to switch luminaires ON/OFF is an expensive solution.