A reader asks:

 How can I tell if the diffusion filter on a particular commercial apparatus is adequate?


There are two issues here. First, you want the screen to project fairly even light, so you cannot see the bare outline of the fluorescent tubes behind it. Second, the screen should not transmit significant ultraviolet (UV) radiation. Almost no manufacturer offers credible evidence of UV filtering; rather, they just make the claim and count on the consumer to believe it.

Technical Details of UV Exposure

One reason for this unhappy situation is that ascertainment of UV exposure is a technical matter — it is expensive to produce the data, and most consumers would not know how to interpret the data. If you are scientifically smart, you can challenge a manufacturer to show you a complete graphical spectral-output curve, starting in the low-UV range (around 200 nanometers) and extending throughout the visible range (up to about 750 nanometers). If there are any prominent bumps in the curve below 400 nanometers, you should reject the device. Two screen compounds, OP-3 and polycarbonate, have been shown to filter UV maximally, so you could look for devices with such screens.