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The 4 Downsides to Sensor-Based Lighting Control

Most of us first experienced lighting controlled by motion sensors in the same place – the toilet.

But since those early days, the use of sensors of all types in lighting control has spread to a wide range of areas and applications.

In particular, two major types of sensors are now frequently seen in office environments: motion sensors or occupancy sensors and daylight sensors or photosensors.

Motion sensors or occupancy sensors are usually linked with a simple on/off response. They turn on when someone is occupying the area, and they turn off when nobody is there.

Daylight sensors or photosensors are usually linked with dimming functions. The idea is that when there is sufficient sunlight in an area, the electric lights can dim a bit and use less energy.

Everything seems so automatic, so easy – but what works in theory often has deal-breaking challenges in practice. Let’s take a look at 4 downsides to sensor-based lighting control in the office.

Downside #1: Limited area of use

Sensor placement and installation are subject to a long list of rules and best practices just to get standard results. One vendor provides installers with a 90+ page guide on sensor placement.

When all factors are considered, only a few areas like toilets and storage closets are suitable for motion sensor use. Daylight sensors are even more restricted – only areas near windows. Moreover, it’s difficult to be confident about your reliance on sensors if so many things can be done incorrectly.

One of our customers installed motion sensors for their meeting rooms. Soon after, they received consistent complaints from several women about the sensors not working. It turned out that the sensors were placed too high and were not detecting relatively short people entering the room. Fixing the problem was time-consuming and costly.

Tired of seeing empty meeting rooms with lights on?
Then our smart lighting solution might help you.

Downside #2: Practical difficulties

There aren’t many things more frustrating than a motion sensor that doesn’t work as expected. Whether it’s because of bad placement, low batteries, or some form of interference, sensors do experience problems from time to time.

These problems can cause staff frustration, energy waste, and worse. In 2010 a guest sued a hotel when she fell and injured herself in the toilet – the motion sensor had turned off the lights[1].

Sometimes it’s not even the fault of the sensors. We’ve seen significant investments in daylight sensors go down the drain because occupants prefer to close the blinds, rendering the sensors useless.

The same can happen with motion sensors. A quick trip to the toilet before heading home in the evening can result in half the office lights turning on for 10 minutes – not exactly energy saving.

Downside #3: Higher costs, longer payback

Adding sensors to your lighting control system increases the lifetime cost of the system.

First, there’s the cost of the sensors themselves. Second, there’s the expertise required to place them and calibrate them correctly, which takes time and money. Third, there’s the ongoing cost of ensuring that your sensor-control layout matches your changing office. Doing this often requires rewiring and relocation of sensors.

If all of this delivers more in extra savings than it does in costs, then it’s worthwhile. The problem is that this is rarely the case. Sensors that control lights in zones usually save LESS energy than individual fixture controls without sensors.

The lack of precision counteracts the benefits of the sensors. And if you install one sensor per fixture, your payback could get even worse. You end up drastically increasing costs in exchange for only minor extra savings. Payback in these cases takes as long as 4-7 years[2].

Downside #4: Lower productivity

To get the most out of your staff, you need to provide a focused environment, a sense of control over their working areas, and a sense of ownership. And yet sensor-based lighting control can detract from this feeling.

It distracts occupants with lights frequently turning on/off. More generally, it subjects them to a frustrating automated system that does not always respond to their needs.

We’ve seen cases where the entire control system has been removed due to occupant dissatisfaction with sensor-based control. Unfortunately, the sensors were the only way to control the lights, so when they were taken out, all of the benefits of scheduling and optimization went with them.

Avoiding pitfalls: do you want sensors, or do you want results?

If you’re considering sensors for your office lighting controls, make sure you understand what you’re getting into. Otherwise, you could end up writing off a significant investment. Sensors have their place in some limited contexts, but the question you must ask is: do you want sensors, or do you want results?

[1] http://www.thompsons.law.co.uk/ltext/lb0410-automatic-lights-toilets.html
[2] Hong Kong Green Building Council. (2013). Section 9.8 Case study for energy saving, Hong Kong Green Shop Guide.