Tweak the Automatic Brightness Levels on your Desire
If you are running CyanogenMod on your HTC Desire and find the light sensor not automatically adjusting the brightness levels to your satisfaction, you can try applying this enhancement tweak.
XDA forum member sfjuocekr has been tweaking the settings for CyanogenMod on the Desire and has helpfully posted the new settings in the HTC Desire General forum.
Settings that can be adjusted includes the window length where when you walk into light, a smaller window length helps increase your device brightness more quickly in combination with a smaller reset threshold.
For more information on the tweak and to discuss results, head on over to the forum thread.