Just changed my light, before and after mesaurements.

Hello all!

I just changed my 65W PC lamp above my 25G tank today, but before I did so I took a light measurement with my Lux meter (out of the water a set distance from the fixture) then I took another reading after replacement.

The change was dramatic.
My old bulb was a year to a year and a half old, on a light cycle of an average of 10 hours on per day.
The measurement was 6,900 LUX

The new bulb was a different brand, but same size and wattage
It measured 10,500 LUX

That's a 52.17% increase in light output.

WOW. It does look visually brighter, but I probably wouldn't have guessed there was that much of a change.
I'll be keeping a close eye on my CO2 levels for the next couple days

Whiskey

 

I thought the general consensus is that over time lamps shift toward the Green spectrum - a spectrum that is bright in the visible ranges, but useless or at least very nearly useless to plants.

Which would tend to mean that the change from the PAR perspective would be even greater than the measurements I was able to take with my equipment.

In any case - your right, the numbers aren't exact, but I think it is still useful information because it reminds us that bulb changes cause significant variation in light, so we should watch the tank closely after doing them to see if other adjustments such as CO2 changes need to be made.
And changing bulbs at least yearly would probably be good practice for plant health as well.

Whiskey