I can pull over a pound in a 4 x 4 with a 600 watt HPS. I don't know what kind of light you're using but one 1000 watt light isn't going to cover the entire 5 x 8 very well. If it's an LED calling itself a 1000 watt but actually only drawing 200 watts you'll definitely need more light.
Don't worry about what others are getting because if you're a novice grower as you say chances are you're not going to get the yields that seasoned growers get. Focus on a successful grow, keep your plants healthy, and harvest what you harvest.