Protractor - describe is not defined

I am using protractor js for testing. When i try to run the test case using

protractor e2e/main/test.spec.js

My conf.js

// An example configuration file.
 exports.config = {
// The address of a running selenium server.
 seleniumAddress: 'http://localhost:4444/wd/hub',

// Capabilities to be passed to the webdriver instance.

baseUrl: 'http://localhost:4000',

capabilities: {
  'browserName': 'chrome',
  'chromeOptions': {
  args: ['--test-type']
  }
},

// Spec patterns are relative to the current working directly when
// protractor is called.
 specs: ['*_spec.js'],

// Options to be passed to Jasmine-node.
jasmineNodeOpts: {
 showColors: true,
 defaultTimeoutInterval: 30000
}
};

I got reference error

> D:\cronj\gxp\10-09-2014\e2e\main\test.spec.js:3
describe('Login page', function() {
^
ReferenceError: describe is not defined
    at Object.<anonymous> (D:\cronj\gxp\10-09-2014\e2e\main\test.spec.js:3:1)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Module.require (module.js:364:17)
    at require (module.js:380:17)
    at ConfigParser.addFileConfig (C:\Users\Cronj4\AppData\Roaming\npm\node_modu
les\protractor\lib\configParser.js:171:20)
    at Object.init (C:\Users\Cronj4\AppData\Roaming\npm\node_modules\protractor\
lib\launcher.js:30:18)
    at Object.<anonymous> (C:\Users\Cronj4\AppData\Roaming\npm\node_modules\prot
ractor\lib\cli.js:129:23)

Could any one help to run the test case using protractor?

You should launch your config file instead of your spec file .

protractor protractor.config.js

In the config file, the "specs" attribute is a glob pattern array that will inject your spec files within the test environment, with the correct definition for objets like "describe" or "it".