LCD brightness?  All of a sudden dull

I built a project based on the LCD tutorial, here: Arduino Tutorial - connecting a parallel LCD and all went well - I was able to print what I needed to my display (one of these: http://australia.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=532-6436).

I just had the screen running for about 15 minutes (arduino plugged into USB as usual) and after leaving the room and coming back in, I notice the screen is very dim. Not a contrast problem, but the backlight has dimmed considerably.

What would cause this? I checked all my connections and everything is the same as it was before, so I can't work out what is happening. Resetting the arduino doesn't fix the problem.

Godge:

I think you may have damaged your backlight LEDs. If you look at page 3 of your datasheet you will see that the white LED Backlight is rated at 3.4v / 20 mA. This means that your backlight requires a current limiting resistor, which does not appear be present on your module. You will need a resistor (around 80 - 100 ohms) in series with pin 15 or 16 of your new module.

Don