Why isn't = working?

What you are trying to use is a conditional operator

== is the correct operator when you are trying to see if something is equal to something else. Putting only one = is for assigning a value to a variable.

Using your code:

if game.Workspace.wing.PointLight.Brightness == 5 then
--I added the second '=' for you, also try to keep 'then' on the same line if possible.
--It is not needed, but it keeps things cleaner.
print 'hi'
end

Let me know if you have any questions!

Note: For more details about this, visit this link http://wiki.roblox.com/index.php?title=Conditional_statement

To see if something is equal to another, you need to use two '='s, like this:

if game.Workspace.wing.PointLight.Brightness == 5 then
    print("Hi")
end

= is for assigning values, you are trying tocompare values, for this you need to add ==

if game.Workspace.wing.PointLight.Brightness == 5 -- If the brightness is equal to 5 then print hi.
 then

print('hi') -- You need to add the brackets otherwise the print will not work
end

Hope this helps!