Factors to consider when specifying a star ceiling
Although highly subjective, the following is a rough guide, based on using a mixture of fibre sizes and a Metal Halide light source
| Typical subjective reactions over large areas | |
|---|---|
| 25 points per sq metre and greater | Dense starfield and Galaxy effects |
| 12-25 points per sq metre | Average starfield |
| Less than 12 points per sq metre | Sparse |
HIGH DENSITY (Kedron Wavell RSL, Brisbane)
When using low output light sources and smaller fibres you will need to increase the point density to maintain a given effect
Small areas can require 2 to 3 times the point density or more to avoid looking "lost"
Higher point densities are obviously more expensive. Night sky effects look better with random point densities and "Galaxy" simulations. Placing higher densities near to light sources can cut costs.
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VERY LOW DENSITY (Caesar's restaurant, Fremantle)
The lowest cost solution is to use all one size and make this the smallest that can be sensibly handled (This is usually .75mm)
Adding more sizes gives a much more realistic night sky effect and gives the opportunity to pick out constellations (e.g. Southern cross)
MANY CONSTELLATIONS (IBM Building, Darling Harbour)
Adding larger fibres adds considerably to the cost and rapidly reduces the number of fibres you can fit in one light source. To the eye there is not a lot of difference between adjacent sizes, so often it is simpler to miss out the next size up e.g. .75mm, 1.5mm, 3mm.
If the budget is not too tight a good starting point is to use an equal area of each fibre vis:
To compare areas with a reference of 100 x .75mm fibres
| Equivalent areas of Optical Fibres | |
|---|---|
| Fibre Diameter (mm) | No of fibres |
| 0.75 | 100.00 |
| 1.00 | 56.25 |
| 1.50 | 25.00 |
| 2.00 | 14.06 |
| 3.00 | 6.25 |
This can be pro-rated for other quantities. Often a good compromise is lots of .75mm with a smattering of larger sizes. The choice is yours.
Normally unjacketed fibre is used, unless installation problems on site preclude this (i.e. The fibre is likely to get badly scratched on site) or the fibre sides will be exposed (say a perforated ceiling). See below for installation considerations.
Fibre can be placed in regular arrays for formal effects (in this case evenness of brightness may be important).
REGULAR ARRAYS (Tugerah)
More usually the effect is random. Try to avoid "tram lines" and obviously bare patches.
The lowest cost solution is a raw fibre end. This works well with a fairly high ceiling (4m and above).
The fibre is cut using side cutters. The distribution of light is generally downwards, but with scatter.
If the fibre can be allowed to protrude 5mm and the sides are visible (raw and unpainted) the tip of the fibre glows and increases visibility.
Ideally for better visibility at higher angles (ie lower ceiling heights) a dispersive bullet lens should be used (not available for .75mm fibre)..
This adds considerably to the cost. Reducing costs by using bullets only on some of the fibres (typically the bigger ones) can be an effective compromise
Recommended light source for all commercial star ceilings is the Arcblaze 150H.
If the ambient brightness is low and the effect is intended to be a background one then de-rating to a DLS75 can reduce costs.
The Arcblaze can drive up to 2400 x .75mm fibres allowing for large areas and large fibres.
There is a large variation in output with these very large common ends. Normally this is an advantage.
If you are using DMX colour wheels or you require a more even result then you need to keep to the equivalent of 700 x .75mm fibres or below.
These very much determine the effects you will get.
For simulations of night skies we normally supply a mesh scintillation effect with chips of vary shades of blue/violet. This gives twinkling stars with flash of blue. (occasionally we include a flash of red if required)
For a more dynamic effect we can supply less white and greater area of colour, with more interesting colours.
This produces almost a swirling effect.
With DMX control we typically supply an extra synchronous motor to drive a mesh (ie black and white) with the DMX control driving the colour wheel.
This gives twinkling stars, with control over the colours (bi colour effects are possible if the motor is stopped partly across a transition)
We can supply a fully finished harness, ready to install. Often this is not practicable.
The usual method of installation is to supply rolls of fibre and all work (including Common End termination) is done on site.
Often access is restricted and the fibre has to be installed into the Gyprock panels on the ground just before they are installed. This requires working closely with the ceiling installers.
We can also supply special systems suited to stretched vinyl ceilings.
If unjacketed fibre is used, then care must be taken to avoid scratching the fibre, typically felt cloths are laid over ceiling members.
Bullet lens are usually used with their bezels. Raw fibre is typically glued into place with PVA glue.
The ceiling is usually painted after the installation of the fibres. Bulleted fibres are usually dropped down and masked. Raw fibres are simply spray painted over (use a water based paint that will not attack the acrylic (always check this!)).
The raw fibre can be finished in two ways, either simply cut with side cutters to expose a fresh end, or
pulled down out of the panel (the PVA will give) by 5mm to expose a clean side and cut using side cutters.
The second method gives better visibility at higher angles.
A GALAXY OF STARS (Hoyts, George St, Sydney)
Other effects worth considering are:
Meteor or comet trails: (sequenced series of points) with or without collisions or explosions
Planets: Internally lit acrylic shapes ie Saturn with it's rings
SATURNS (Blue Fin Fishing Club, Inala)
Information on the complete range of Digilin Fibre Optic products is avialable from their website at www.digilin.com.au
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