Measuring UV Light Output

From time ago, I was wondering about a system to measure to UV output of the several lamps I have available in my studio, as well as how much it lasts a given lamp to be stabilized with a constant output power. There are in the market some specialized UV light meters to do those tasks. Devices with a variety of modes, from measuring the UV light output to control a given selected UV dose. But in general its price is over the range of $250-$350. Probably the investment is worth, but it is also true that those measures are only necessary as a first approximation to a new lamp. Once the lamp is characterized, there can be a long time with no more measurements. At the other extreme of possibilities is the trial and error method, but this option is only apparently cheaper, because of the necessary materials and time consuming.

Searching for cheaper options, I decided to try with a sort of UV meter intended to control the risk of hazard by the Sun UV radiation. and bought in eBay the Smart UV Meter . It is a little cylinder that must be simply plugged into the headphone jack of the smartphone. We need in addition the corresponding smartphone app Smart UV Checker. Total cost is US$29.99 + shipping. The Fig., 1 shows the meter plugged on an iPhone6S.

As a test to know which is the minimum time necessary to achieve a constant UV output, I placed the device under the BLB fluorescents bank. As because of the device size, iPhone plus the meter, it cannot be placed under the UV bank in the operation position, then it was simply placed at a fixed distance (Fig., 2).

The app allows for a continuous measurement. With this option activated, have been noted the indicated value at 1min intervals after the lamps were on. The measures obtained were:

Table 1

As can be clearly seen in the Table 1, after some time in between 2 and 3min, the output is stabilized. For practical purposes, a 3min of lamp heating will be safe to ensure reproducible exposures. The device is sensible enough to detect little output differences in the spaces between each other fluorescent tube. If a change for new tubes is expected, a previous measure of comparative outputs can be very useful to determine the exposure time for the first test.