Yes, there is but it is very indirect light. On previous roof light attempts, I have actually had the top of the dash and instrument binnacles lit up which is a real pain. Now all I have is the front area of the road and truck illuminated. Not through reflection or anything, just by way of general illumination. The shrouding of the lamp and the shape of the light 'cone' means that I have managed to avoid glare, which is what I think that we are really talking about.
Chris
Chris
Job done 
And would look really good on a white truck 
