It’s useful to measure the output of an Ultraviolet light source when shooting UV Fluorescence and UV Reflected photography. There are a number of UV meters on the market, very expensive. This post is about, as usual, a budget solution that goes for $150 on eBay.
UV meter and filters for multispectral imaging. From left to right: B+W 486, B+W 420, Heliopan RG1000, B+W 403.Below there is a scan of its quantum efficiency curve. Quantum efficiency means that on the Y axis there is the percentage of light detected for each wavelength.
Quantum Efficiency Curve (sensitivity in percentage) for the budget UV meter.Testing a budget UV meter
I like whenever possible to test my new equipment. I don’t have any expensive spectrometers, so I’ll have to play with my filters and figure out alternative testing methods.
First, we need to check if this UV meter actually measure only UV light. It turns handy what said about the white LEDs in this post. I tested the UV meters with my set of filters. For a recap of my filters set, see here. As usual, a movie:
Let’s test it step by step.
1. With the white LED light lamp on and without any filter, the reading is 10 microW. This could be due to UV, VIS and IR light. Though, we know from this post that white LED have some infrared light component other than visible. So, we have to find out if this reading is due to VIS or IR. let’s proceed with another filter.
2. B+W 486. With the B+W 486 filter on the lamp, reading is 0 microW since this filter cut any IR and UV. So, we understand that the reading is not due to VIS light but to IR. Indeed, the quantum efficiency curve, provided by the manufacturer, goes up until 480 nm, and doesn’t tell anything about the IR…we could stop our test here but let’s try the other filters.
3. Heliopan RG1000. This is a far IR pass filter and reading is 0 microW. Indeed, the close IR from the LED lamp is cut off by the RG1000, which cut IR until 1000 nm.
4. B+W 403. Eventually, with the B+W 403 filter we read 1 microW. but this is due again to the closest infrared light that this filter allows through.
In conclusion, this is a fine UV meter, we just need to put on it a X-Nite CC1 that stop IR but it’s transparent to the close UVA. We really need this filter on if we are testing a UV lamp that emits also IR (which is the case with Wood’s glass).
