You might have seen these around the house. They’re called blue wool dosimeters and we use them for keeping an eye on how much light exposure the house gets over a year. In February we have to collect them in and send them off to be analysed.
They are rather low tech, but very clever. They are made of picture mount and pieces of specially dyed (blue!) wool, the latter which is known to fade at a certain rate when exposed to light.
We use them to see how much light falls on certain objects or rooms over a whole year. As a registered museum we need to try to keep to museum standards of light exposure to our collection:
- highly light sensitive rooms/objects = 150,000 lux hours
- moderately sensitive rooms/objects = 600,000 lux hours
Blue wool dosimeters allow us to see how much cumulative light the house and collection has been exposed to over the year and if we need to adjust how we show the house.
You can see below that the aperture is smaller than the piece of fabric so when they are analysed there is something to compare the faded area against. We need to make sure that the dosimeters aren’t moved to make sure they give the most accurate information they can.
Sometimes, as they are wool, they get munched by pests – wool is a favourite food of carpet beetles and their larvae, woolly bears…