There are many, many threads about Shellac and whether you need the lamp, etc. etc.
In short, yes you do need the Shellac White lamp or the grey Brisa Lamp. These are the only two lamps which will cure Shellac.
Many people will tell you that you can use any lamp for any gel and that it is only a way of suppliers making you spend more money. However you will not know by looking if your gel or Shellac is cured correctly. Is it really worth risking an insurance claim if a client gets over exposure due to uncured gel.
Use the Search and have a look at other Shellac lamp threads. There is also a Shellac Group which is a wealth of information too.