Photoelectric Sensors

What are they?

Photocelectric (PE) sensors that detect light level  and can be used to turn off or dim lights in response.

Advantages / Disadvantages

Energy is saved through automatic dimming.

A low cost feature, this typically achieves payback in less than 5 years.

Best applied to large open spaces as spaces with complex fitout – or individually operated internal blinds – will rquire large numbers of sensors to cover each unique space.

Can be frustrating for tenants if lighting levels keep changing (on sunny / cloudy days).

If used to turn lights on and off, this should only be done in low sensitivity spaces such as warehouses and lobbies

Certain lamp types such as hibay lights used in warehouses may not be well suited to daylight control due to the characteristics of the lamp.

Energy efficiency

Photoelectric l sensors can reduce the energy consumed by artificial lighting close to windows. Artificial lighting in areas more than a few metres from windows  (distance depends on window height) will not benefit from photocell  sensors as natural light will have negligible impact in these areas.

Savings achieved with photoelectric sensors in offices are far less than those achieved by occupancy sensors, so the latter should always be considered as the first priority.

Running costs

Photocell sensors require periodic checking and recalibration to ensure they are functioning correctly. Overall running costs will reduce due to the energy savings achieved.

Retrofit / improvement opportunities

Photocell sensors typically need replacement every 15–20 years.  Photocell sensors can be easily retrofitted to modern lighting systems and can be fitted out of hours to minimise disruption to the tenants.  Photocells are only applicable for lights adjacent to windows or skylights.

Applicable buildings

Photocell sensors are applicable to a wide range of building types and are commonly used in open plan offices adjacent to windows.  Buildings with good levels of natural light will particularly benefit.

Floor plate implications

Spaces with complex fit-out are poorly suited to the use of photoelectric sensors.

Occupant comfort

Photoelectric sensors will prevent the areas adjacent to windows becoming  too bright by reducing artificial lighting levels accordingly. Natural light is considered to improve wellbeing. An override switch should be provided so lights can be kept on when required, for example, for viewings when  letting a space.

Maintenance implications

Photocell sensors have low maintenance requirements but need to be kept clean. The operation of the sensors should be routinely checked.


Sensors situated close to the perimeter of the floor plate and either mounted high on the wall, in a suspended ceiling or as part of a  light fitting.

What to ask for

  • Does the perimeter lighting have photoelectric sensors in place?
  • How do the lights responds to the photoelectric sensors – by switching or dimming?
  • When were the photocell sensors last checked / maintained?

More information

References required