An “age old problem” when using Film or TV based arc lamps is the issue of turning the light source off and on, because of the start up cycle which can take 5 minutes to reach full colour temperature, a good solution is to equip such a lamp with a mechanical dimmer, or Dowser Shutter.

 

This was the starting point at the London 2012 Olympics that needed to provide instant on/off control of a large amount of lighting.

 

Based on initial guidance from the hire company proving the lighting, an important factor was that the Dowser should default to open and that it could be as simple as a shutter pivoting into the light path.

 

Specialz prototyped a simple shutter mechanism to determine how well this could be controlled and how it would stand up to the heat. This prototype was automated using a high performance solenoid with a power reduction circuit to maximise the initial reaction time and then hold the Shutter in place with the minimum of effort.

 

Initially the lamp in need of the Dowser was a 575W HMI profile spot with a 210mm / 8” diameter, this range soon extended to a 1200W with a 250mm / 10” diameter and a 2500W with a 320mm / 12.5” diameter, meaning that there would have to be three different sizes.

 

This lead to more prototyping to see whether the additional load of the larger shutters or the heat from the bigger lamps would cause any issues. Fine tuning of the various components was required to ‘stretch’ the simple principle and prove that it could work.

 

Each Dowser would also have to incorporate a mounting plate to attach to its lamp and a method to attach the lamp’s barn doors to the front face of it.

 

The design that emerged was a unit that could be mass produced and quickly assembled and because of the effective power handling, many units could be run together without using much power.

 

These Dowsers are now available to be purchased from Specialz.

 

Design Features:

Shutter operated Dowser

Spring return on shutter – default to open

Simple transit strap for shutter

Mains input (DC energised solenoid with power reduction circuit)

Mains output (to next unit)

Easy interface to lamp gel frame holder

Captive Barn Doors interface on front via easily removable single component

Safety attachment point

Black anodised shutter

Lightweight Aluminium frame