Everything under control?

Simple on/off switching, dimming or fully networked controls? Dr Jones takes a look at the range of technological options available to specifiers

Which types of controls are suitable for modern interior lighting systems?

To answer this, we’ll look at the most popular element of lighting controls, rather than trying to cover all the technologies and topologies.

First, let me discuss the key properties of light that can be controlled in modern general lighting systems.

  • The amount of light when the light is turned on.
  • Whether the light is on or off.
  • The colour temperature or chromaticity of the light.
  • Other aspects such as pulsing of the light source.

There are key components in the lighting system that control the amount of light, turn it on or off in response to manual and automatic interactions, and more elaborate systems can adjust the colour of the light to suit a particular environment.

Simply on or off

The simplest lighting system is configured as shown in the graphic.

The light is driven directly from the mains through a switch that simply turns the light on or off. This relies on the fact that the lamp has a set of electronics built into it that translates the mains supply into a useful supply for the light-emitting part of the lamp, whether that be an LED, CFL or tungsten filament source. This is referred to as a self-ballasted lamp.

If the lamp or luminaire has no built-in power supply, a separate component takes the mains supply and converts it into a useful controlled current for the light-emitting device.

So the electronics – called the control gear, either built-in or external – is a key control in the system that takes one form of electrical supply and converts it to another (usually a voltage conversion) and then controls that supply to ensure that the light level is maintained in a way that avoids unwanted flicker or variations. In the case of discharge lamps such as ceramic metal halide or fluorescent, the electronics also start the lamp, and then control the current through it.

Different terminology is used in the industry to describe the control gear used for different types of lamp technology. ‘Transformer’ is used to provide a low-voltage supply to halogen lamps, ‘ballast’ is used for most discharge lamps and the term ‘driver’ is used for LED lamps. Each performs a similar function: they change the input (usually mains) supply into a form that the lamp technology can safely and reliably deal with.

To dim or not to dim

The next interaction will be to decrease the light level from the nominal maximum, known as dimming. Dimmers come in many shapes and sizes and can be manually or automatically adjusted.

The dimming instruction for a manual system can be carried on the same wire as the mains supply – ‘in-line’ dimming. This is achieved by chopping up the mains AC signal, thus providing less power to the light. The manual settings are provided by a switch that is operated by hand. Of course, the ultimate dimmed light source is one that is switched off and dimming switches offer this option, of course.

Automatic systems rely on some external input to make a decision about what to do with the lights and this is where sensors and external controls become important. The main input types to the dimming or on/off process are:

  • timer circuits,
  • presence or proximity sensors,
  • daylight or ambient light sensors,
  • alarm signals, and
  • programmable events.

These sensor or input circuits will respond to certain inputs and create an output signal that can be interpreted by the control gear to alter the drive conditions of the lamps, usually reducing the power into the lamp.

A special type of control is found in emergency lighting in which disruption of the power to the main luminaire causes a battery-operated circuit to become active, powering an emergency light.

Shaken or stirred

The alteration of the drive conditions to dim lamps can be achieved in a variety of ways, depending on the lamp and electronics. Each one enables a change in the light level in a controlled manner in a defined relationship with the dimmer input signal. There are different dimming methods for each lamp type. A system schematic for this more complex arrangement is shown below.

Networked solutions

When dealing with large numbers of luminaires or lamps in different locations, there are a number of networked technologies that control the light level of individual lights. Scenes are set by controlling lights in relation to each other to create a visual effect. Two of the most popular systems are DMX512, which is a standard for digital communication networks that are commonly used to control stage lighting and effects. The other is Digital Addressable Lighting Interface (Dali), which creates a flexible, cost-effective and decentralised lighting system. Dali was developed to replace the older analogue 1-10V dimming system. However, 1-10V is still highly popular for lower-cost systems.

Click the image to enlarge

The wheat and the chaff

When it comes to light measurement, not all photometers are created equal. Which one should you use if you want to improve your luminous metrology?

The doctor will see you now…

There’s no getting away from it, lighting is a technical subject. But you don’t need a physics degree to understand it all – you need the doctor. Dr Gareth Jones, that is, one of the UK’s top experts. Send your questions to thedoctor@archive.luxmagazine.co.uk. Next!