Just changed my light, before and after mesaurements.

Whiskey

Member
Jun 14, 2010
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San Diego, CA
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
 

SuperColey1

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Feb 17, 2007
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That's a 52.17% increase in light output.

No it s a 52.17% increase in brightnesss for a human eye :)

The actual light (PAR) may be increased but may not. I would suspect it has gone up a bit but no necessarily as much as you measure with the Lux. That may be due to the colouration changing through use.

AC
 

Whiskey

Member
Jun 14, 2010
368
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San Diego, CA
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
 

SuperColey1

Guru Class Expert
Feb 17, 2007
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Well I've been suggesting that the actual drop off even in Lumens for modern lighting is nowhere near that a tube needs changing yearly. maybe more than 3 years with only 5% loss for a linear NO on an electronic ballast.

No idea on CFs though.

Not sure on the shifting part. I would expect it to be the other way myself as old lamps tend to look yellower than white and therefore I would assume it is moving down the K rather than up it. As I say I have no idea on this.

Lux and Par can mean similar thing except that if a bulb was say 6500K the lux would be high, If it then veers down to reds the lux will be significantly lower. Doesn't mean the PAR will be though. May even mean there is more PUR if the light is moving away from non usable light like ultra vioulet etc.

AC