Why does this loop do this ?

What i want it to do is just go from 0 to 0.30 and keep repeating but they just go to -1 then back to 1 why does this happen ?

glow = script.Parent
num = 30
while true do
    for i = 1, num do
        glow.Transparency = 0+i/num/1
        wait()
    end
    for i = 1, num do
        glow.Transparency = 0.30 - i/num/1
        wait()
    end
end

The answer is simple. You just got some math incorrect:

glow = script.Parent
num = 30
while true do
    for i = 1, num do
        glow.Transparency = 1/(num/i)
        wait()
    end
    for i = 1, num do
        glow.Transparency = 1/(num/i)
        wait()
    end
end

You should really improve your math skills. It would help a lot.