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Light fittings commonly used in portable accommodation are 5ft long T12 or T8 tubular fluorescent lights with a rating of 65W and 58W. A cabin of the size ISO 8ft * 20ft * 8.6ft is in general fitted with 3 lamps and a cabin of the size ISO 8ft * 40ft * 8.6ft is generally fitted with 5 lamps.
T8 lamps are used as replacements for T12 lamps in the same switch-start luminaries. They save up to 10% of the energy consumption while giving 10% more light. [1] We suggest replacing all T12 and T8 fluorescent lamps by T5 lamps which have even higher efficacy. However, these lamps require different fittings as they are shorter in length (4ft). The following table lists properties for all three types of tubular fluorescent lamps. To determine the total luminaire power consumption both lamp and control gear power have to be taken into account. For high intensity discharge lamps the lamp power should be multiplied by 1.1. [3]
Lamp properties [1] [2]
Light fittings used in some site accommodation do not feature diffusers. Light is illuminated straight from the light tube and therefore can cause glare. We suggest using luminaries with diffusers. This allows the light to be better dispersed within the room, but reduces the light output slightly.
The following two example studies will demonstrate to what extent the energy demand for lighting can be reduced by replacing currently used fluorescent tubes with 36W tubes.
Example – One Cabin
Assuming a 9.5m * 3m cabin is fitted with 5 tubular fluorescent lamps which are constantly switched on for 11 hours per day. The electricity costs are assumed to be 10 pence per kWh and the CO2 emissions associated are 0.93kg per kWh when the electricity is supplied by a diesel generator working with an average efficiency of 27%.
The following table compares the illuminance, electricity demand for lighting, energy cost and CO2 emissions associated over a period of one year (2860h) of using 36W, 58W and 65W fluorescent tubes.
Illuminance, energy demand and carbon emissions
Using 5 lamps per cabin provides a more than sufficient illuminance for all 3 types of fluorescent tubes, since the illuminance required is 200 lm/m2 - 500 lm/m2 (dependent on the area of use). Installing T5 lamps in the cabin can reduce the energy demand by 38% compared with T8 lamps and reduce demand by 45% compared with old T12 lamps.
Example – Xscape site
Providing switch-start fluorescent lights with 4ft fittings and 36 W lamps in all of the 26 LORS cabins on the Xscape construction site, Laing O’Rourke achieved an annual saving of £900 in comparison to some of their other construction sites where fluorescent lights with 5ft fittings and 58W lamps are still installed in all cabins. Thus the annual carbon emissions associated with lighting could be reduced by 8368kg.
Taking into account the complete life cycle there are other environmental benefits of using T5 lamps. T5 lamps have lower carbon emissions and a lower mercury content compared to the other light sources. The small product dimensions result in less material, packaging, weight, transport and recycling volume. It can be said that the environmental impact of the complete life cycle is lower for T5 lamps than it is for their predecessors.
The initial costs of 58W and 36W fluorescent lamps are similar. In some cases T5 tubes are even cheaper because of their slightly lower illuminance.
D122 Fluorescent Electronic Batten/Diffuser (OSRAM) 4ft 36W white £18.97
As mentioned before we suggest installing lights with diffusers in order to avoid glare.
(1) Energy Saving Trust, Energy Efficiency Best Practice in Housing – Energy efficient lighting; March 2004 (2) http://www.li, v.ac.uk/abe/students/modules/arbe211/electric_lighting.pdf (3) Commission of the European Communities, Energy Efficient Lighting in Buildings, Directorate-General for Energy (DGXVII) (4) www.osram.com/lightatwork/light_room/optimaleslicht/steue
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