The light on usb drive is still on after umount

When I use umount to unmount my usb drive, the light on the usb drive blinks and after that the light is still there (without being turned off like what you normally see on M$ Windows system). When I check my FreeBSD system (FBSD 7.2), there's no usb device so I guess the usb drive has exactly been unmounted successfully. But then why is the light on the usb drive still on? Is it safe to remove the usb drive in this state?
Yup, it is safe to remove it. When you unmount a file system, you do just that - unmount the file system. When you eject a drive in windows, windows unmounts the file system and sends a command to the device to detach or switch off, something which isn't strictly necessary.
Incidentally, if you are running FreeBSD 8.0 and would like to achieve the same effect, after unmounting the file system use usbconfig(8) to send a power_off command to your device:

usbconfig -u 2 -a 3 power_off

2 and 3 is the address of the USB device - something you can get by running:

usbconfig list