You can determine that with a good light meter. Take a reading of foot-candles with new bulbs then read later after , say a year and see what it produces.
You can determine that with a good light meter. Take a reading of foot-candles with new bulbs then read later after , say a year and see what it produces.
Did I mention that I don't trust my light meter? Oh yeah....I don't trust my light meter and I never really use it....but it would work for the purpose of measuring foot candles of a new bulb and later throughout the year.