Bishop Museum

The building

The Bishop Museum stands in Kalihi, on the Honolulu side of the valley, in a group of dark basalt buildings begun in 1889. It holds the largest collection of Hawaiian and Pacific cultural material anywhere in the world.

Light is the conservator's problem, not the visitor's

Museums measure light in lux and then in cumulative lux-hours, because light damage is cumulative and it does not reverse. Nothing that has faded comes back. The materials in a Hawaiian collection sit at the most sensitive end of that scale: feather work, kapa, plant-dyed cordage and fibre, textiles, and organic natural history material. Conservation practice puts the most vulnerable of those at around fifty lux, and daylight arriving through an untreated window is orders of magnitude above it.

Ultraviolet does the most damage per unit of energy and is the first thing to control, but it is not the whole story: visible light fades dyes as well, and heat and swings in relative humidity accelerate everything. A gallery with sun coming through it is running all four mechanisms at once.

A historic building narrows the options further. The window openings are original, and in places so is the glass. Replacing glazing on an elevation like that is an argument with a preservation officer before it is a construction job, and hanging shading outside is worse. Meanwhile visitors quite reasonably expect a gallery in Hawaii to have daylight in it.

What window film does about it

A film applied to the interior face of the existing pane removes effectively everything below 380 nanometres — the whole ultraviolet band — while changing nothing about how the window looks from the outside. That combination is what makes it usable on a protected building, and it is reversible: the film can be removed and the original glass is as it was.

Where the visible and thermal load also has to come down, a spectrally selective film reduces total solar energy and visible transmission together, which lowers both the fading rate and the temperature and humidity swing the collection experiences through the day.

It is one control among several, and it should be described that way. Film does not replace lux monitoring, rotation of sensitive objects out of daylight, case glazing or blinds, and no film makes a daylit gallery indefinitely safe for the most sensitive material in a Pacific collection. What it does is remove the most damaging part of the spectrum permanently and cheaply, and buy the collection time — which is the thing a collection actually needs.

There is a building-fabric argument alongside the collection one. Thick basalt walls hold temperature well, but the windows are the weak point, and the solar gain coming through them is what drives both the daily temperature swing and, with it, the swing in relative humidity that organic material responds to. Reducing the gain at the glass steadies the interior between the times the plant is running, which is worth as much to a gallery as the peak reduction is.

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