Three ways to light a library

Lux's technical editor Alan Tulla looks at three ways to approach lighting libraries

Libraries aren’t what they used to be. My local public library is now called a Resource Centre and whilst the new name may upset the some people, 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 are now full of computer screens. These are almost certainly positive polarity with black lettering on a white background. Some might have 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 in cd/m2) of the luminaires where they might be reflected in the screens.  There are recommended limits in BSEN 12464 and the Code for Lighting. 

It may seem obvious, but people do a lot of reading in libraries, maybe 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 surfaces. The recommendation in the SLL Guide Lighting for Education, is 200 lux on the shelving near ground level. All the options shown exceed this by at least 25%. 

In terms of the luminaire layout, I was talking to a lighting engineer who works for a major supermarket and the issues involved in lighting the library shelves are almost exactly the same as shopping aisles. 
One solution 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 light on the tops of the shelving. One other solution is to fit luminaires to the tops of the shelves on short outreach arms.

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 ceiling height of 4m in the main area and 7m adjacent to the window wall. The overall floor plan is 25m wide by 18m, excluding the entrance

Where there is a limited budget, the most cost effective solution may be to retrofit on a one for one basis. This uses the economical MODLED 600 mm x 600 mm recessed panel. This is designed to be quick to install and commission. It is available in different lumen outputs so that in a one for one retrofit situation, you have a choice of the final illumination level.   

The architecture of this library is such that there is a much higher space adjacent to the entrance. Previously, this was unlit but now we have brightened the area using the large Capo pendant unit. This is a decorative unit where you want a lot of light output (8,000 lm – 24,000 lm) with an attractive appearance. 

Since there is a lot of daylight, the Capo pendant units have been switched off via a photo sensor linked to the lighting control system.

Tech spec
  • Luminaires
  • MODLED Slim panel plus large Capo XL pendant
  • Optical control
  • Diffusing panel and opal refractor
  • Arrangement
  • 7 x 8 array
  • Average horizontal illuminance on desk
  • 440 lux, average vertical on book shelves: 370 lux
  • Installed electrical load
  • 4.5 W/m2
  • Pros
  • Economical to install

 

Libraries often have high ceilings or double storeys with mezzanine floors. Here, the 4m ceiling is an ideal opportunity to use suspended luminaires. The MODLED Suspended Through Wire comprises a basic 1,200mm module. There is a wide range of joining and corner accessories so that continuous lines and shapes can be configured. You can make squares, rectangles or build them around features such as stairs. 

Here, we have use them in groups of three with a space between. The rows are staggered in order to “break up” the layout on the ceiling. This is a simple technique for improving the appearance of a space without using any more luminaires.  

Again, we have the large Capo XL adjacent to the window wall but since there is no daylight, they are switched on and produce about 400 lux at floor level.

Tech spec
  • Luminaires
  • MODLED Suspended through wire
  • Optical control
  • Diffuser
  • Arrangement
  • Staggered rows
  • Average horizontal illuminance on desk
  • 365 lux, average vertical on book shelves: 278 lux
  • Installed electrical load
  •  4.1 W/m2
  • ProsFlexibility with modern appearance

This is maybe my favourite option. As in option B, we have used the suspended MODLED Through Wire but this time, we have arranged them in two large squares (approximately, 4m sides) over the book shelves at the rear of the library. This gives good vertical illumination on the shelves facing all directions. 

You can see that the computer screens are clustered in the foreground.  Here, we have used a luminaire dedicated to screen use, the Rubix Surface. This has nine square cells with semi-specular aluminium reflectors. These meet the 3,000 cd/m2 requirement of BSEN 12464. An interesting feature of the Rubix is that the cells are surrounded by a backlit diffuser giving a softer “halo” effect. 

In the area adjacent to the window wall, we have used the smaller output Capo, 3,000 lm – 4,500 lm. This is a highly efficient unit and delivers almost 100 lm/W.

Tech spec
  • Luminaires
  • MODLED Suspended plus surface mounted, nine-cell Rubix
  • Optical control
  • Various
  • Arrangement
  • As shown
  • Average horizontal illuminance on desk
  • 480 lux, average vertical on book shelves: 336 lux
  • Installed electrical load
  • 4.3 W/m2
  • Pros
  • Good for digital and print