Interesting comments...
A mate bought some expensive l.e.d. conversions for his B.M.W. 'bike and without any doubt they were far brighter than standard, so, ever the cheapskate I got some bulbs from Ebay. I tried mine in the Herald, Harley, and even the Scoobydo pick up and in all cases the results were rubbish and could hardly be seen. The worst was in the Harley rear light which is a custom type and the bulb lies across the lens rather than in line, invisible for all practical purposes. Mine cost a couple of quid tho', mate's cost about ten times that...
One of mine is now in the back of Albert the Ariel where it is substantially better than standard, hmmm?