piritinoanswered grow question 5 years ago If you don't have a lux meter, you can try downloading an app that performs this function to your smartphone. it is not 100% reliable but you can still get an idea if you have a good smartphone. in the first days your seedling needs at least 4000/5000 lux to grow so I advise you to approach the lamp and try with your smartphone to help you adjust the distance.