Light sources in exhibition design – part 2

Creative use of small fluorescent bulbs at a Venice Biennale

Light sources in exhibition design | Part 2 – Fluorescent and Metal Halide lamps

Fluorescent lamps
Fluorescent light sources are a large family of different lamps, available in very various shapes, linear, circular, and globular, and with a great variety of sockets.
A fluorescent light works by converting the ultraviolet light emitted by an electrically excited gas (originally Neon) into visible light by a surface-deposited phosphor.

Their high luminous efficacy, usually around 80 lumens per watt, and long working life are greatly appreciated in exhibition lighting, despite being not the best when chromatic rendition is taken into consideration and thus inappropriate for direct illumination of, say paintings.

However, fluorescent lamps are a very good resource for many exhibition-related applications, such as making light boxes and large light-emitting surfaces or for object lighting, if color accuracy is not fundamental. Fluorescent lamps have been also widely used in large lighting installations, because of their low surface temperature, long life, and reduced specific electrical consumption. Nevertheless, the recent introduction of improved LED lamps (for example arranged in LED strips) provides today an interesting alternative to fluorescent lamps, mainly due to LED’s lower maintenance costs.

Circular fluorescent lamps combined with geometrical polycarbonate diffusers

Linear fluorescent lamps used for showcase illumination

Metal-halide lamps
Metal-halide lamps (MH) are often used to create diffuse illumination in exhibition rooms and galleries.
MH bulbs are part of the gas discharge lamps family, in which light is produced by exciting the electrons of a gas through an electric discharge (the light is actually produced when the excited electrons re-descend to a lower energy state, releasing a photon).

Together with high-power halogens, they are the most powerful lamps suitable for interior applications, and among the most efficient and long-lasting.
Unfortunately, their typical spectrum, due to its strong emission peaks at very specific wavelengths also for “natural light” lamps (which generally means lamps labeled to have a color temperature of 2800K-3000K), makes them not suitable for illuminating artworks for which a correct color rendition is mandatory.

Another drawback of unshielded MH bulbs is their prodigious emission at short Ultraviolet wavelengths, which always requires the addition of a UV filter to prevent damage to artwork.

The typical spectrum of a metal halide lamp, showing emission peaks at specific wavelengths

Consequently, HMI lamps are typically for creating diffuse background lighting to be completed with directional lamps providing better chromatic performance, such as narrow-beam halogen spotlights.

Metal-halide lamps have been adopted in this museum to create a background lighting of a temporary exhibition room

Light sources for exhibition design part 1
Light sources for exhibition design part 3