How to Light

Design Clinic: Three ways to light a library

A library with three different lighting designs
In a library it’s important to minimise the viewing intensity of the luminaires where they might be reflected in the screens. There are recommended limits in BS EN 12464 and the Code for Lighting.

EOS logoLIBRARIES HAVE changed. Many have been rebranded as ‘resource centres’ and whilst this may upset the fogeys (of any age) it does reflect the change inside. If you are designing the lighting for a library, you need to consider what people will actually be doing other than just looking for a book. 

One major difference is that libraries now have a lot of computer screens. These are almost certainly positive polarity with black lettering on a white background.

Gone is the older negative polarity software, or even micro-fiche, where white lettering is seen against a black background. In either case, you need to minimise the viewing intensity (strictly speaking, the luminance cd/m2) of the luminaires where they might be reflected in the screens.  There are recommended limits in BS EN 12464 and the Code for Lighting. 

It may seem obvious, but people do a lot of reading in libraries, maybe much more than they do at work.

If ever there was a ‘paper based task’, then this is it. Related to this is that older people require higher levels of illumination than younger ones. Depending on who uses the library, you will be designing to 300 or 500 lux. 

Of course, libraries still have plenty of bookshelves and you need to light their vertical faces. The recommendation in the Lighting Handbook is 200 lux on the shelving near ground level although this may be difficult to achieve with narrow aisles.

Interestingly, I was talking to a lighting engineer who works for a major supermarket and the issues involved in lighting the shopping aisles are almost exactly the same as library shelving.
One solution is to fit luminaires to the tops of the displays. Another is to run rows of luminaires parallel to the aisles. This requires quite a specific geometry to the reflectors and mounting height to avoid wasting light.

Another is the ‘cross-aisle’ solution which is much more forgiving in terms of layout and geometry.  The disadvantage is that you lose some light on the tops of the shelving. 

The main point to remember is that libraries are much more multi-function spaces than they used to be. Think about what people actually do there and design the lighting accordingly. 

Our library has a 3.4m ceiling height and the area you can see in the rendering is about 15m wide by 14m to the back wall.

Option A: Comfort 810

This scheme is simplicity itself – it uses just one type of recessed ceiling mounted luminaire. The Comfort has a pmma lens over each individual LED and these are located in 25 cells, 5 x 5. Despite the panel being only 42mm deep, the drivers are integral and can be connected to the mains without the use of tools. The main body of the Comfort is white, self-extinguishing polycarbonate and has a steel gear box enclosure. 

The 810 is available with a cut-off of 43 or 76 degrees to minimise reflections in display screens. The 21W version has a UGR, Unified Glare Rating, of less than 16 so it is ideal where there is a large number of computer monitors or where avoidance of glare is at a premium. The higher output 28W produces a UGR of <19 so it still fully complies with BS EN 12464 for use in offices and other indoor spaces.  

The Comfort is also extremely efficient delivering almost 160 lm/W. 

At-a-glance Tech Spec A
Luminaires: Comfort 810
Optical control: Closed cell plus pmma lens
Arrangement: As shown
Average horizontal illuminance on desks: 495 lx.
Pros:  Simple and effective  

Option B: Athena Direct/Indirect

Wherever you have an office type space with a ceiling height typically above 3m, you can always achieve a good-looking result using suspended direct/indirect luminaires. Here, we have used the Athena suspended approximately 800mm below the 3.4m high ceiling.

The big advantage is that this solution directs about a third of the light on to the ceiling and thus makes the space appear more airy. 

The Athena is just 60mm wide and fitted with cross-blade louvres which can be either black or white. An interesting option for the Matrix is that the body is available in a range of bright colours so it can enliven the whole space or be used to differentiate certain areas. 

We have arranged the luminaires over the bookcases in a ‘cross-aisle’ solution. This gives you plenty of flexibility in terms of adjusting the spacing of the book cases. It is also useful where the location of the bookcases is only temporary. There is a minor disadvantage in that you lose some light on the tops of the shelving.

At-a-glance Tech Spec B
Luminaires:  Athena
Optical control: Cross-blade louvres
Arrangement: As shown.
Average horizontal illuminance on desks: 540 lx.
Pros:  Light and airy 

Option C: Piazza plus Evo

This makes more of a visual statement and has a more contrasting appearance. We have used the recessed Piazza in combination with the Evo spotlight. The Piazza panel is used to provide a safe background ambient illumination whilst the Evo draws your attention to the more important areas. 

The Piazza is a backlit panel. I.e. the LEDs are above the diffuser. This is more optically efficient than equivalent sidelit panels. It is also fitted with an opal diffuser and a micro-prismatic film which enables the Piazza to achieve uniform, glare-free lighting with a UGR of <16 in most locations. 

The Evo is a high output track mounted spotlight with a choice of five beam angles from 13 to 64 degrees. Couple this with its output of 2,600 to 3,700 lumens, this is more than some ceiling panels, and you have and extremely versatile spotlight. There is a choice of colour rendering, CRI, either 80 or 90. 

At-a-glance Tech Spec C
Luminaires:  Piazza, left, and Evo spotlight, right
Optical control: Micro-prismatic, opal and specular reflector.
Arrangement: As shown
Average horizontal background illuminance: >250 lx.
Pros:  Versatile

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