Just replaced a 1.5 year old PC Bulb - light increase.

[Whiskey]

This never ceases to fascinate me.

I replaced my 1.5 year old PC bulb today, with another identical bulb. I took light readings with my LUX meter, the meter was positioned at the bottom of the tank, and the probe was not moved while I was changing the bulb. I gave the new bulb about 10 min to get warmed up before taking the reading.

Old bulb: 3200 LUX
New Bulb: 4400 LUX
That is a light increase of about 37% just by changing the bulb.

So if you have any old bulbs out there, you might want to think about swapping them out.

Whiskey

 

[Tom Barr]

Clean the old bulb and then measure the light difference, the new one is clean, the old one often have lime and water splat on them etc.

10-20% is typical for cheapy bulbs, higher grades might do better.