Daytime Dimming Photocell

IDU600 Daytime Dimming Photocell (Patent Applied For)
Up to 25% of the energy consumed by traffic lights can be saved by dimming the lights during dull daylight hours.

Traffic signal intensity is set to ensure that signals remain visible against their background under the brightest most extreme conditions (daylight levels >40,000 Lux) likely to be met on UK roads and allowing for the problems of dazzle caused by low sun.

Away from these extreme conditions there are plenty of occasions where the ambient light level is well below summertime peaks. Since signal visibility depends on the contrast of the signal against the background, a signal dimmed to 25% of its bright output will be as visible against a 10,000 Lux sky as a bright signal will against a 40,000 Lux sky.

Data from the UK Meteorological Office confirms that during 38% of daylight hours, the ambient light levels are below 10,000 Lux.

The Radix Traffic IDU600 Photocell is a direct replacement for the existing photocell (dusk to dawn only dimming) and will offer significant cost savings on either metered signal sites or through the provision of a new Elexon code for the additional dimming regime. It will also extend the life of halogen signal bulbs by approximately 26%.

Principle of Operation

During daylight hours, if the ambient light level is less than 10,000 Lux and the sun is at least 15 degrees above the horizon, then the Radix Traffic photocell switches the traffic signals to the dim state (conducting the 230V or 48V signal to the controller).

The new photocell will also switch the signals to bright/dim in exactly the same way as the current dusk to dawn switching regime.

The IDU600 photocell has been designed to work with all existing traffic control systems requiring only the selection of a 230V ac or 48V ac variant for LV and ELV sites respectively.

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Daytime Dimming Photocell IDU600 Daytime Dimming Photocell IDU600

For a Local Authority with 190 tungsten halogen sites (total junction and pedestrian facilities), paying 10p/kWhr, the 25% saving on their energy bill equates to an annual saving of approximately £12,800.

When reporting the energy use of their traffic signals equipment it will be necessary for Local Authorities to change the Elexon coded dimming regime for those sites that have the new photocell fitted. This regime will encompass the greater levels of dimming than just the night time hours normally used.

To estimate the annual savings that can be made for your Local Authority using the Radix Traffic Daytime Dimming Photocell, a cost saving calculator can be downloaded from the product downloads page.