Some leg ulcers do not seem to respond that well to the standard treatments that we currently use. One reason for this may be that there are high levels of bacteria in the ulcer which may be slowing down the rate of healing. Because we need to be careful about when we use antibiotics, this study will look at another way of killing bacteria in the ulcer. This new method involves putting a special gel on the ulcer and then shining a particular type of light (visible red light) onto the ulcer for a short period of time.