Does anyone use a light meter?

Detritus Mulm

Guru Class Expert
Jun 12, 2005
When I replaced the bulbs for my T5 HO unit, I ended up with 28W bulbs instead of 54W bulbs? I noticed because the Ludwigia started to suffer. I stuck a watt meter on the fixture and it was only drawing about 100 watts for 4 bulbs (I have 8), so I increased the duration and # of bulbs I was using. I normally only run the daylight bulbs part f the day to simulate dawn/dusk.

But now I'm having a BBA issue, so I put the watt meter on the bulbs again and it's reading over 200 for 4 bulbs. So is it possible that the ballast switched gears based on the age of the bulbs or is it more likely that I'm senile and they were always putting out 54W? I mean it's bright, but not as bright as the original 54W bulbs. Plus the bulbs are 4' and the tank is 3', so the plants aren't getting a full dose. I plan to cut them back in any event.

But I wondered how efficient any given bulb might really be for a given ballast? Does anyone use a light meter to verify their effective light or just replace as usual?