You can't tell by the serial numbers. Prices on seconds are $70 US dollars. Firsts are like $120 - $160 USD.
The best method is where and when did you get them??
Mr. Gransee is such a perfectionist, that there is very little difference between firsts and seconds (minor blemishes, anodize mismatch, slightly off center beam, and such). The primary difference is that seconds have no warranty. Seconds also come as a kit: head and all battery holders.
If you got them from a dealer, then it is likely that you got firsts.
