We've discussed using smartphones to measure light in the past, so this caught my eye. Lumu, via Kickstarter, is claiming an add-on hardware piece for your iPhone, currently $99 during the campaign.
The main drawback I see is that it "only" goes down to .15 lux, which isn't quite as low as I've measured in actual scenes during tests. However, it also lets you record location and voice notes with each reading, which could be immensely useful in site surveys.
Would you use it?