the designer's choice for the workplace

The choice of fluorescent lighting within the office environment may seem like a simple decision for the Lighting Designer. However this decision has been consistently challenged over the life of my career in lighting, with the more creative Lighting Designers constantly wanting to introduce differing lit effects and lighting technologies into the workplace.

When I agreed to write this article I thought do I recognise this term "fluorescent lighting"? The answer was yes but not as a term used by lighting professionals but as a term used in a derogatory sense by the general public. So does "Fluorescent Lighting" have an image problem.

When discussing workplace lighting with office workers, usually the first statement they make is that they would prefer something other than "fluorescent lighting". On closer investigation what the majority of the public believe you mean when you talk about fluorescent lighting is a regular array of luminaires, mounted on or within the ceiling plane, resulting in harsh and unflattering lighting. These schemes are normally acceptable with daylight from side windows to give additional illumination to vertical surfaces. Architects and Interior Designers also tend to perceive "Fluorescent Lighting" as a low quality lighting solution.

However the Lighting Designer will probably be envisaging a much more positive outcome choosing from a variety of luminaire styles with differing lamp formats, electronic or high frequency (possibly dimming) control gear, high colour rendering lamps and variety of lamp colour appearances to suit the situation. In the face of this opposition, how can we justify that a lighting solution predominantly utilising luminaires with fluorescent lamps is the correct decision for the majority of commercial and a good proportion of industrial lighting applications?

Fundamentally it comes down to the photometric requirements of the lamp / luminaire package, the required illuminance levels and luminance patterns required in the workplace to provide a comfortable visual environment.

Unlike other internal spaces the lighting requirement for visual comfort within the workplace is normally successfully achieved with a predominately diffuse lighting scheme with slow rates of change in luminance. To achieve this large surface area lamp sources like fluorescent lamps are preferable due to their already semi diffuse nature rather than being intense point sources such as HID or incandescent lamps. If working on a project with a ceiling height of 3m or greater then uplighting maybe appropriate with HID or high power compact fluorescent lamps. This height is exceptional in the UK with the average ceiling height being 2.7m in commercial offices making both uplighting and indirect/direct lighting problematic without some additional modelling of the ceiling.

The vast range of fluorescent lamps (the current Osram catalogue has 72 pages devoted to fluorescent lamps) enables the designer to choose the lamp parameters to suit each individual situation. Physical size, lamp brightness, colour temperature, colour appearance, colour rendering, ability to dim etc. are all definable characteristics by the designer. Choice of these parameters, in conjunction with the choice of luminaire will fundamentally affect the lit appearance together with the cost / energy through life of the installation.

To give an actual example of this I was asked to design a scheme for an open plan office area, by changing the type of lamp, control gear and maintenance regime, affected the design such that the quantity of luminaires varied from 16 to 27, for the same maintained illuminance figure.

The styles of fluorescent lamps are not comparable when one looks beyond the basic lamp efficacy lumen/watt figure. Characteristics such as lamp wall brightness; luminous area and lamp direct flux ratios need to be considered when choosing the most appropriate lamp. These factors are normally referred to as bare lamp photometry. The orientation of the lamp can be an issue due to the bare lamp photometry. For example T5 versus T8 Eco tubular lamps. We have been told by the lamp industry that T5 is the way of the future and we should use it in preference to the T8. I would challenge that basic premise when compared with the Triphosphor Eco Lamp. The lamp wall brightness of any style of 16mm fluorescent lamp needs to be controlled. This control is by a secondary photometric material whether it be a diffuser, reflector or a controller this material obviously reduces the LOR of the luminaire whereas the T8 lamp can be viewed directly, if so desired. The T5 lamp has an optical advantage in that its smaller diameter is more like the theoretical linear source. This smaller lamp allows a greater optical efficiency however this results in higher patch brightness which may need to be controlled and hence negate the gain in efficacy.

This variance in luminaire efficiency has been addressed to a degree by the Part L of the Building Regulations "luminaire lumens/watts" requirement and the BREEAM requirement for a minimum luminaire Light Output Ratio of 0.6. We are therefore legally required to assess the combined lamp/luminaire package as a whole from an energy efficiency standpoint.

With the advent of computer working within the office we have to consider the luminance patterns across multiple fields of view, not just the horizontal but the vertical as well and the CIBSE LG3 Amendment 2002 acknowledges this with its requirements for wall and ceiling illuminances to be 30% and 50% of the working plane illuminance. It should be noted the original LG3 always suggested illuminating other surfaces to minimise static and dynamic luminance imbalance and hence reduce eye strain. To reduce the LG3 to "500 Lux Category 2" clearly misses the point.

We also should be looking to challenge the concept of an average maintained illuminance across the working plane. This arrangement can be replaced with workstation based lighting with a lower overall level of illuminance for circulation purposes, say 200lux. Overall maintained illuminance normally consumes between 12-16w/m2, a workstation-based scheme will consume between 8-10w/m2. These workstation based schemes have a high level of user satisfaction with the individual being able to customise their lighting environment to their own requirements.

With the dual threat of Global Warming and Global Dimming we need to be ever more aware of energy use and even small gains in efficiency whether it is from lighting or any other form of consumption need to be taken. I would suggest that fluorescent lamps represent the considered choice for the workplace and it is the Lighting Designers' responsibility to come up with schemes that excite architects and deliver visual comfort to occupants

With the considered use of the correct lamp within a suitable luminaire we can raise the public's perception of "fluorescent Lighting".

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