[Chris Langton]

Chris Langton  asked the Naked Scientists:
   
How do you measure the UV output of a fluorescent lamp or a high intensity discharge lamp?
Thanks

Chris Langton

What do you think?

[techmind]

If you want to know exactly what the lamp is emitting, you'd use an instrument called a spectrophotometer. This measures the intensity of the light source wavelength by wavelength. Internally, the instrument splits the light into its constituent colours (strictly wavelengths) using a diffraction grating (has a similar effect to a prism, but has a number of advantages), then measures the intensity using a 1-dimensional CCD array. Conceptually such an instrument just has a long line of light-sensors placed along the "rainbow" from the "prism" and so measures the light-intensity of each "colour" (including infra-red and ultraviolet - beyond the extremes we can see).

You can then compare the emission of the lamp against the sensitivity of the human skin for sunburn purposes ("erythma"), or against known fading of inks or dyes or whatever the problem at hand is.

A simpler and much cheaper device is a basic (or UV-enhanced) photocell with a UV passing filter in front of it - and can be sufficient for a specific predetermined task (eg erythma dose) but will not analyse the wavelength-by-wavelength emission of the source for analysis after the measurement.