comScore, in collaboration with the Havas-owned digital agency Media Contacts, took a step towards defining “heavy” and “light” online video watchers today, and in doing so showed how power users are skewing at least one stat.

The two companies looked at the time people spent watching online video and broke down their findings into:

• Heavy viewers (top 20 percent of viewers): averaged 841 minutes of online viewing per month
• Moderate viewers (next 30 percent): averaged 77 minutes per month
• Light viewers (bottom 50 percent): watched only 6 minutes per month

By comparison, comScore found that in the record-breaking month of December, the average viewer watched 203 minutes of video. So heavy users are blowing the curve by racking up all those hours, while the remaining 80 percent are watching less than half of what the “average” is.

This study echoes another recent study comScore participated in that showed “heavy clickers,” who represent just 6 percent of the online population, accounted for 50 percent of all display ad clicks.

Jarvis Mak, Media Contacts’ vice president, U.S. director of research and insights explained the wide discrepancy between heavy and light viewers during a keynote presentation in New York yesterday, noting that a similar gap existed between heavy and light web surfers back in the early days of the Web.

In a separate study also released today, Nielsen Online found out when people are watching online video. Tuning into network TV web sites is most popular at lunch time, between 12 p.m. and 2 p.m., while UGC attracts night owls, with more people watching those sites on weekends, between 11 p.m. and 6 a.m. This makes sense given that UGC stuff can run a little too risque for work.