Can't Install lessc using NPM on mac - node.js

Question

I was trying to install lessc globally on my mac, I installed node.js from their website, and when I run the command (npm install -g less) I get this, could you please help me, all I want to do is to install Less and get the less2css compiler on sublimetext 3 work properly:
npm install -g less
npm WARN locking Error: EACCES, open '/Users/Mohammad/.npm/_locks/less-c2213c903e2e7354.lock'
npm WARN locking at Error (native)
npm WARN locking /Users/Mohammad/.npm/_locks/less-c2213c903e2e7354.lock failed { [Error: EACCES, open '/Users/Mohammad/.npm/_locks/less-c2213c903e2e7354.lock']
npm WARN locking errno: -13,
npm WARN locking code: 'EACCES',
npm WARN locking path: '/Users/Mohammad/.npm/_locks/less-c2213c903e2e7354.lock' }
npm ERR! Darwin 14.4.0
npm ERR! argv "node" "/usr/local/bin/npm" "install" "-g" "less"
npm ERR! node v0.12.7
npm ERR! npm v2.11.3
npm ERR! Attempt to unlock /usr/local/lib/node_modules/less, which hasn't been locked
npm ERR!
npm ERR! If you need help, you may report this error at:
npm ERR! <https://github.com/npm/npm/issues>
npm ERR! Please include the following file with any support request:
npm ERR! /Users/Mohammad/npm-debug.log
MacBook-Pro:~ Mohammad$ npm install -g less
npm WARN locking Error: EACCES, open '/Users/Mohammad/.npm/_locks/less-c2213c903e2e7354.lock'
npm WARN locking at Error (native)
npm WARN locking /Users/Mohammad/.npm/_locks/less-c2213c903e2e7354.lock failed { [Error: EACCES, open '/Users/Mohammad/.npm/_locks/less-c2213c903e2e7354.lock']
npm WARN locking errno: -13,
npm WARN locking code: 'EACCES',
npm WARN locking path: '/Users/Mohammad/.npm/_locks/less-c2213c903e2e7354.lock' }
npm ERR! Darwin 14.4.0
npm ERR! argv "node" "/usr/local/bin/npm" "install" "-g" "less"
npm ERR! node v0.12.7
npm ERR! npm v2.11.3
npm ERR! Attempt to unlock /usr/local/lib/node_modules/less, which hasn't been locked
npm ERR!
npm ERR! If you need help, you may report this error at:
npm ERR! <https://github.com/npm/npm/issues>
npm ERR! Please include the following file with any support request:
npm ERR! /Users/Mohammad/npm-debug.log

Answer 1

You need to execute this command as superuser if you do not have write permissions on the /usr/local directory.
Please try:
sudo npm install -g less