yellow spots...i think its from light or heat

im getting yellow spotting on some of my leaves. its like they are dried out, when the tip of a leaf turned yellow it broke off so i think i have my light too close i will adjust and see what happens. if anyone thinks its anything else please let me know. just for future reference how close should i have my light and should i change the distance during the differant stages? the plants are almost a month old... thank you.

there is a faq here...

http://boards.cannabis.com/grow-faqs...ce-plants.html

are the tops burnt??? fan leaves show plant problems and a picture paints a thousand words...