The wavelength is the same. It is the contact time that makes the difference.
Keep in mind that ponds are operated in direct sunlight and at much lower turnover rates. The ratings on pond UV's are very different but can be used on aquariums. As stated previously, in aquariums, we constantly introduce the risk of parasites and other nasties. To use a pond UV in your tank, you will want to slow the flow through the sterilizer. Find the rating (pump flow, and UV Watts) for that sterilizer and the one recommended for your tank. You can tailor it using a bypass valve to control the flow and contact time, or you can use a dedicated pump for the sterilizer.
A missmatched UV sterilizer is better than no sterilizer at all.