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Design Clinic: corridors

Top lighting consultant Alan Tulla sets his sights on corridor lighting in the second of his articles presenting alternative ways to light a particular type of space

Last month’s Design Clinic looked at small offices. Now let’s turn to another area badly in need of more attention: corridors. And for those of you who only read executive summaries: the 18W CFL downlight is dead.

Although the task requirements for corridors are not onerous, they are often illuminated for long hours. They don’t generally get any daylight and long corridors, especially, can appear gloomy. Installing movement sensors and dimming will make a massive difference to the amount of energy consumed.

The three options set out here are intended to show how the appearance and running costs of corridor lighting can vary depending on the method and choice of luminaire. The corridor I’ve chosen to look at is 1.8 metres wide and 2.8 metres high. The calculations are based on a 24-metre-long space to demonstrate luminaire spacing and light distribution patterns. All the designs achieve about 150 lx at floor level. Energy load is quoted per linear metre because, unless the corridor is very wide, you’ll only be using a single row of luminaires.

The conventional off-the-shelf solution

This design uses a conventional recessed downlighter with a horizontally mounted 18W compact fluorescent lamp (CFL). For our 24-metre corridor, the downlights are spaced at 1.2m intervals. Although CFL downlights may appear the same, their efficiency (in terms of light output ratio and delivered lm/W) can vary enormously. The unit used here is an old design and delivers just 39 lumens per circuit watt. This efficacy is way below the level recommended in the current Part L and even further away from the 60lm/W in the proposed 2013 version.

On the plus side the appearance is generally bright and uniform, although the upper sections of the wall are quite a bit darker than the floor. The colour the walls are painted will make a big difference to the overall appearance of this scheme. But it uses far more energy than our other two options and has no special features to commend it.

Tech spec

Luminaire Typical off-the-shelf recessed 225-250mm-diameter downlighter with white bezel ring and horizontally mounted 18W CFL
Optical control Specular aluminium reflector, no cover lens
Arrangement 20 luminaires in a single row down the centre of the corridor at 1.2m intervals
Maintained average illuminance at floor level 165 lx (100-150 lx on wall)
Overall uniformity on floor >65%
Electrical load 15W per linear metre
Total equipment cost £756

Pros Inexpensive to buy and available everywhere with a large variety of embellishments and accessories
Cons Heavy electrical load compared with other solutions. Many downlights on offer do not meet current Part L. And it looks dull

Efficient LED fitting displaces the CFL downlight

This type of highly efficient LED downlight with precise optic finally marks the end of the 18W CFL downlight. The LEDs use less than half the energy of the budget option, produce almost the same illumination level and give better uniformity.

This option also has the lowest energy and maintenance requirements of the three options. For an LED downlight, it has a wide beam and puts a lot of light on the wall. Typically, 100-150 lx is achieved at eye height and below. Inevitably with a small, powerful source and specular reflector, there are some strong highlights on the wall but the corollary is that a degree of sparkle livens up the corridor.

Tech spec

Luminaire Inperla C2 HR LED downlight emitting 2,000 lm
Optical control Specular aluminium reflector, no cover lens
Arrangement Eight luminaires in a single row down the centre of the corridor at intervals of approximately three metres
Maintained average illuminance at floor level 155 lx (100-150 lx on wall)
Overall uniformity on floor 75%
Electrical load 8.7W per linear metre
Total cost £1,120

Pros The best option for energy saving and maintenance
Cons High capital cost

T5 fluorescent throws light on the wall

This is my favourite way to light corridors. The scheme uses recessed asymmetric wall washers and the highest illuminance is on one wall. Most corridor walls nowadays carry notice boards. In prestige offices, the walls often have corporate art or graphic design. It makes sense, therefore, to put the greatest illumination on the wall.

This scheme uses recessed mounted T5 fluorescent units at 3m spacing. Note that there is no need to place the luminaires down the centre of the corridor. Placing the luminaires closer to the wall, at a distance of, say, 600-750mm, would highlight the wall even more but at the expense of uniformity. Hospitals will often offset luminaires in corridors, so any patients lying on trolleys on their backs don’t have lamps shining straight in their eyes.

Visually, the scheme works well because it gives good vertical illumination, not only on the wall but on people’s faces. The ceiling is also lighter with this layout than with the other two options. Maybe surprisingly, this scheme also gives the highest horizontal illuminance on the floor and the gradation of brightness from wall to floor makes the visual field more interesting.

Tech spec

Luminaire Recess mount Trilux Solvan C2-L RAX with 35W T5
Optical control Asymmetric semi-specular aluminium reflector, no cover lens
Arrangement Eight luminaires in a single row down the centre of the corridor at intervals of three metres
Maintained average illuminance at floor level 210 lx (185 lx on wall)
Overall uniformity on floor >60%
Electrical load 12W per linear metre
Total cost £816

Pros Stimulating, useful for highlighting notice boards and graphics, offers the highest illuminance on walls and floor and a 25% energy saving over the 18W CFL scheme for only a small increase in initial cost
Cons Uses more energy than the LED option


LUX VERDICT

Regular Lux readers will know that I am not easily impressed by the performance claims of LED products. But there’s no doubt that the latest versions of quality LED downlights beat their CFL equivalents by a significant margin.

If you want to light a corridor, there has to be a very good reason why you wouldn’t use an LED downlight in preference to a compact fluorescent one. But let’s face it, a recessed downlight scheme is never going to make a big impression or wow a client, LED or not. For that, the wall-wash option may be a better choice. It consumes only a little more energy than the LED downlight and looks miles better.

Next month: large open-plan offices
alantullalighting.com

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