Non-radioactive alarm clocks

Today I was at some department store looking at the clocks.  They had some nice alarm clock models, but I noticed one brand Rhythm in particular... their models had these specially painted numbers that glow in the dark.  Yeah, many clocks do that, but the strange thing is I noticed that this brand's clocks came with a sticker that reads "Non-Radioactive".  WTF?

That reminded me a long time ago when I saw bottled water, and on the label it was written "0 calories".