Residential Lighting – a case study
Jonathan Greenstein , EDS Engineering October 2001
The client has a large residence of about 400 square meters on one floor, plus a roof library and garden. There were about 500 lighting units throughout the apartment – three quarters of them consisting of dichroic spotlights.
The client complained about the continual need to replace bulbs and connectors which, apart from the cost, was very disruptive, as the residence is used for both living and for a large amount of entertaining.
After analysing the problem, we isolated the following issues:
After revamping the whole system, the customer has had almost three trouble free years. From changing 5-10 bulbs a week, he now changes probably no more than one a month. He’s delighted with the overall lighting level and quality. His fuses rarely trip, and his art collection and library are on proud display.
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Types of bulb
An odd collection of lamps had been used throughout the house.
Bulbs of different manufacturers and different quality within the
same manufacturer had been used in the same area. The result was
also so non-uniform as to be downright ugly. The use of cheap
bulbs meant that after say 1000 hours, the reflectors were
discoloured and the light output adversely affected both in terms
of quality and quantity.
Dichroics were used in all the spots even though some positions, due to their proximity to inflammable materials, clearly called for non-dichroic units.
Bulbs with a beam spread of 36-38 degrees are the most common, but for some areas, 60 degrees gave a better spread. In the library, we used additional glass diffusers to further soften the light. These simply fit over the dichroic bulb face. 20watt and 50watt dichroics are common in Israel, but 35watt are difficult to obtain. These we imported direct from the UK. The general price in the UK for dichroics is less than half the price in Israel.
Until the last few years, bulbs rarely had built-in UV filtering. Since this residence has a nice collection of paintings and rare books, it was imperative that the lighting, which is left on for many hours daily, did not cause any UV damage. All bulbs had to have UV filtering built in or provided for by glass filters.
Colour rendition was very important particularly for illuminating paintings. The quality of the Osram Titanium range is truly spectacular. However, these units have a reddish sideglow that is visible in open glass units, and so there were places that we chose to use Philips instead for their whiteness.
POWER SUPPLY
If there’s one thing that’s sure to cause the premature demise of a bulb, it’s overvoltage. All the low-voltage for the lighting in the flat had been provided by heavy step-down transformers. These are totally unsuitable for halogen lighting. We measured voltages of up to 14.5 volts on some of the lamps.
The worst, case scenario is when two 50 bulbs are fed from a single 100watt transformer of this type. The regulation in any event is poor, but when one of the bulbs burns out, the output voltage shoots up and damages the remaining bulb. Single transformers are called for. The ideal being a good quality electronic type where the voltage is well clamped to 12volts. The 50 watt normal transformers on the market, apply somewhat less than 12volts and although this extends the life of the bulb, it lowers the colour temperature. Quality electronic transformers have built-in short circuit and thermal protection.
In our workshop, we subjected one high quality transformer to a continuous short over a period of 24 hours with no affect.
MAPPING
Even though we tried to avoid specifying too many different types of bulbs, we ended up with about ten different types. Our fear was that whoever changes the bulbs, might put in the wrong type, defeating the whole purpose of our planning. To avoid this, we gave each type of bulb a letter from A to K. The whole flat was mapped out and all the light positions marked on the plan with the letter denoting the correct type of bulb to be used.
All the bulbs are kept in clearly marked drawers and the stock is always kept well stocked.
SUMMARY
Three years on and everything is running smoothly. Very few bulbs burn out prematurely, thermal shock is a thing of the past. When the bulbs reach the end of their useful life, the bulbs in the whole area together with the bulb holders are replaced in one session. The lighting is very effective, the maintenance costs are down 80% and the client is happy. The only losers are the bulb manufacturers.