Twenty feet -- that's six meters. Other suggestions include putting more distance between you and the device and using good lighting.

VOA: special.2011.08.01

I wonder if there's some UV light out of this new lighting set up in our classroom here.

好的，我想知道这里,我们教室里的这套新的照明装置,是否有一些紫外光出来。

麻省理工公开课 - 化学原理课程节选

This modern festival of African-American culture includes lighting candles each night from December twenty-sixth through New Year's Day.

VOA: special.2009.12.21

And as the country prepared for a period of mourning, people were seen lighting candles and placing flowers in front of the Presidential Palace in Poland's capital Warsaw.

VOA: standard.2010.04.10

In contrast,a light bulb has much more impact in the use phase, where it's using the energy, and where you can reduce that with more efficient lighting technologies,"

VOA: standard.2009.03.30