okay so here it is my freinds and i were all sitting around playing cards and smoking cigarettes and it dawned on me that i did not know the real difference between “light” and regular cigarettes??? that’s my question… 
A light cigarette has slightly less nicotine, CO, and other pollutants. In Canada the ‘toxic emissions / unit’ must be listed on the side of the pack, so its pretty easy to tell (don’t know 'bout american smokes, I don’t smoke 'em)
A quick look at two packs, one ‘light’ & the other ‘extra light’ (ok not a perfect match to your question, but it’s what I got on hand) shows ‘tar’ to be 12-32mg for the light, 10-34mg for the extra light; nicotine 1.2-3.0mg for the light vs. 1.0-2.8mg for extralight; CO 12-32mg light, 9-28mg extra light, etc.
That being said, health-wise the difference is negligable. I think the biggest difference is in the harshness or ‘flavour’.
Matches.
besides a difference in tobacco blends, there is one other difference. Take a look at a light cig just past the filter. You will see a row of tiny holes running around it. This lets air into the cig other than that drawn in through the lit tip. Therefore you are getting less smoke in each puff than you would without the holes.
Extra air holes in the filter and less licorice flavoring in the tobacco.
If I grasp the theory correctly, the ‘light’ cigarette does have the holes in the filter as mentioned, but they are ineffective.
The holes cause the machines used to test tar & nicotine levels to draw in a modicum of straight air, rather than pure smoke. In real life, a human smoker closes off these holes with their fingers and/or the air channels with lip pressures while smoking.
This fact, plus some nasty additives, cause ‘light’ cigarettes to be somewhat more hazardous to smokers than regular filtered cigarettes.