copy this script:

function ligh()
startx=tpt.mousex
starty=tpt.mousey
--tpt.create(startx , starty , "BRAY")
raditus=math.random(1,100)
angle=math.random(0,360)
targetx=startx+(raditus*(math.cos(angle/2)))
targety=starty+(raditus*(math.sin(angle/2)))
tpt.create(targetx , targety , "BRAY")
tpt.drawline(startx, starty, targetx, targety,255,0,0)

for i=1, 2 , 1 do
startx2=targetx
starty2=targety
--tpt.create(startx2 , starty2 , "BRAY")
raditus2=math.random(1,50)
angle2=math.random(0,360)
targetx2=startx2+(raditus2*(math.cos(angle2/2)))
targety2=starty2+(raditus2*(math.sin(angle2/2)))
tpt.create(targetx2 , targety2 , "BRAY")
tpt.drawline(startx2, starty2, targetx2, targety2,0,255,0)
for i=1, 2 , 1 do
startx2b=targetx2
starty2b=targety2
--tpt.create(startx2b , starty2b , "BRAY")
raditus2b=math.random(1,50)
angle2b=math.random(0,360)
targetx2b=startx2b+(raditus2b*(math.cos(angle2b/2)))
targety2b=starty2b+(raditus2b*(math.sin(angle2b/2)))
tpt.create(targetx2b , targety2b , "BRAY")
tpt.drawline(startx2b, starty2b, targetx2b, targety2b,0,0,255)
end
end
end
tpt.register_mouseclick(ligh)

then save it as "ligh.lua" in the powder toy directory,then run the script,when you click the mouse,it will create lightning!(just line,and will also create BRAY points at all points which the lightning turns.)