Sunday, June 09, 2013

UV Beads: How to See Ultraviolet Light Indoors

In a bout of paranoia and curiosity, more so the former, beads were ordered years ago. These were not ordinary beads though, these were beads with some sort of dye that were supposed to react to ultraviolet (UV) light. They are designed for kids and kiddy level science experiments dealing with UV rays.

UV Spectrum and UV Beads

According to Science With Toys at Wikispaces, the dye in these beads react to UV light between the 300-360nm range. Also stated in the site are the spectrums for UVA (320-400nm) and UVB (280-320nm). The band below 280nm, UVC, should be blocked by the atmosphere except where there are holes.

Without UV light present, the beads should be a grey/white color. When exposed to sunlight or other artificial sources of UV light, they should start lighting up. From my experience, my collection of beads light up with color to varying degrees depending on the amount of UV light present. For example, outdoors in the shade, they are very lightly tinted, whereas they become dark colored once I expose them to direct light. This same behavior is noticed on overcast days (one massive "shadow").

Protected from UV light indoors?
It should supposedly be common knowledge that UV light makes it indoors. I've read a bunch of articles saying that people should be putting sunscreen on even if they spend their entire day indoors. Obviously, how much UV light gets in depends on how much sunlight gets in, or usually, how many windows there are. Way back when, someone told me that windows blocked UV. Apparently, that's true and false and somewhat in between. 
My research suggests that the amount of UV light that gets indoors depends on the materials of your windows. There are no solid rules like plastic or glass blocking entire wavelengths of light. Different types of glass, plastic, laminates, and other layers block different things. There are materials that can act as filters for specific ranges of radiation that can be installed on things. Think UV filters for cameras and windows.

UV Beads Indoors
So, I decided to test out how much UV got into my house. This was a pretty simple setup that involved putting some UV beads in direct sunlight near a set of windows. Two of the windows were replaced last year and one set has been around forever. The old pane has two layers of glass and was installed at least two decades ago. This is important because newer windows may be somewhat better at blocking UV. The curtain being moved is in front of the older set of windows.

From the test, the UV beads appeared to light up a bit the second the paper or clipboard is removed. That suggests that UV gets in through the windows. Once the curtain was moved from the older windows, the beads got a lot darker. I've never seen these beads light up in the dark or at night, so I'm guessing it's the UV.

UV did appear to get in through my set of windows. Again though, the amount, if any, that gets in depends on the exact composition and construction of the windows. There should be purpose-built UV filters available on the market.

Unfortunately, because the beads react to a fairly broad spectrum of radiation (300-360nm), I don't know if the windows block UVA or UVB. The different bands apparently cause different reactions in humans.

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