Things Every Lighting Practitioner Should Know About Lighting Controls, Part Four

In this four-part series, Charles Knuffke, Systems VP & Evangelist, Wattstopper/Legrand, North and Central America and past chair of the Lighting Controls Association provides a crash Lighting Controls 101 class for lighting practitioners. Originally published as the Controls Column in LD+A Magazine in 2023. Reprinted with permission.

This is the fourth and final article in this series covering the basics of lighting controls every lighting practitioner should know. We’ll finish up by covering two last input devices: timeclocks and daylighting controls.

Timeclocks

While the original timeclocks were mechanical devices, the most prevalent method for time-based control in our industry uses an electronic clock chip, often embedded in a load control device like a wall switch, load controller, relay panel, or in a front-end device when there’s a room-to-room network on the project.

While many timeclocks use standard time events—often accepting either AM/PM or 24-hour format—some allow the timeclock’s location to be input to calculate an approximate time for dusk and dawn. While there are several different definitions of dusk and dawn, we also have to recognize that the earth isn’t a perfect sphere and that the presence of mountains, trees, and other buildings may require a facility engineer to adjust these times for their site. A timeclock capable of doing an astronomic function may therefore include an “offset” so that lights can be turned On a few minutes before/after dusk, and Off a few minutes after/before dawn.

A key consideration is interface. Some timeclocks use a 7-day weekly repeating schedule to control loads with a set of commands each individual day of the week, ideal for regimented occupancy. Others allow the input a string of days, times, and actions, often referred to as an event-scheduler format. And the format for inputting data can vary—from simple text entry to interfaces similar to Microsoft Outlook. Seeing information graphically allows spaces with regularly changing schedules—e.g., a ballpark—to be easily updated by the facility engineer.

If there are multiple timeclocks on a single networked system, an important requirement is ensuring that they’re all set to the same exact time. Individual timeclocks might sync to a primary timeclock in the system or to a specific computer’s time setting, or, if the system has access to the internet, a query using the Network Time Protocol URL.

While all timeclocks should be able to turn Off lights, many applications may prefer manual On (local switch/dimmer) for these loads. The manual-On feature has been long present in smart timeclocks and ensures that lights don’t turn On automatically in a building that will be unoccupied for that day.

Note that timeclocks may do more than just control loads—a powerful capability resides in systems that use time-of-day commands to send a system into “normal hours” versus “after hours” sequence of operation, with more aggressively energy-saving operation after hours.

Now a few additional notes on energy codes. It’s worth asking how a system handles interior lighting requirements concerning a manual override after the lights have been turned Off. Typically, any lights that are turned On after an Off command can only stay on for two hours, and then ideally will warn the occupants that unless they re-enter an override their lights will go Off shortly. Some codes have an exemption to the two-hour max override, but they require a captive key switch to be used to keep the lights On until the key is removed from the key switch, but this exemption is typically only allowed for specific applications.

Lastly, be aware that your local energy code probably requires that there be a battery backup for the clock chip of a certain length of time, so even a full-day power outage shouldn’t cause the device to lose its time setting when power is restored. Also, since it’s possible that daylight savings events may be changed in the future, make sure that any new change—from the “spring forward” date being changed to a new date, or Daylight Saving being done away with completely—can be handled easily by the timeclock in your system.

Daylighting controllers

When dealing with timeclocks, we benefit from the fact that we’re only interacting with a single consistent dimension: time. With daylight, however, three dimensions are required to describe that space in addition to time, as well as the hardware that will be located in the space. Energy codes are harmonizing daylighting zone and rules to a significant degree, but rooms aren’t just a simple box with a window. The furniture, mounting of the general lighting, window shades if applicable, time of day, and more all can impact the success of a daylighting system.

The complexity of daylighting systems stems from application. While the goal is to determine the amount of daylight illuminating the task level in a daylight zone, placing a sensor on the task surface would invite occupants to impact its reading. To avoid possible occupant interaction, the industry, for the most part, mounts daylighting sensors on the ceiling. There are exceptions to this which I find very exciting, but we’ll focus on the more prevalent ceiling-mounting method.

Once the daylighting sensor is mounted, it may be specified as open or closed loop. In a closed-loop system, the sensor is placed where it reads the sum of the daylight and the electric light. By going through a calibration sequence of turning the electric light On and then Off during daylight hours, the amount of daylight reaching the sensor can be determined via the difference. Depending on other values, the sensor can then reduce the electric light based on the daylight and monitor the changes. These changes are seen by the sensor, so a feedback loop is established, hence the name “closed loop.” One benefit of a closed-loop sensor is that it may have a very simple calibration routine, but one drawback is that two daylighting sensors in the same space controlling different daylight zones might not be communicating, so they may end up influencing each other. Also important is making sure that these sensors are not directly above an indirect luminaire. When in doubt, refer to the manufacturer’s instructions.

In an open-loop system, the daylighting sensor mounts by a window or skylight where ideally it only reads the daylight at that specific location. To calibrate the room, usually a light meter takes a reading at the task while the electric lights are On and another while they’re Off. At each step, in addition to recording the light meter’s reading, the sensor records the level of light it’s reading. The purpose of this is to define the mathematical relationship so if you know what the daylight sensor reads, you can determine the light at the task level. A drawback to the open-loop approach is that a light meter is usually required, but a benefit is that in a space with both a primary and secondary daylight zone, a single sensor can control both.

Note a major goal of a daylighting system is to have minimal effect on the occupants in the space while controlling the general lighting. For this to occur, the lighting should be dimmable. Previous attempts at daylighting with On/Off, or bilevel or trilevel lighting steps were barely acceptable at the time, but there’s no reason to be doing this control now. Newer codes even require the general lighting in daylit zones to be dimmable. I also appreciate that Title 24 allows occupants a temporary override of any daylight sensors—something I wish other codes would consider.

Get control

When I set out to answer the question, “What is the minimum that every lighting practitioner should know about lighting controls?”, it set off quite a journey of exploration. With just these four columns, lighting practitioners can establish quite a strong foundation for working with stakeholders, asking the right questions, and of course learning more.