Some Data on PC Bulb Life

[VaughnH]

Another member of our local aquatic plant club did some PAR meter measurements of his various 55 watt PC bulbs. His light fixture has 6 bulbs, and they have been in use for varied times, so this data is interesting. These are PAR meter measurements right at the bulb surface:

Two things stand out: One is that the bulbs seems to lose about 25% of their light intensity very quickly, and the other is that they seem to last at least 2 years at the somewhat lower intensity, before continuing to lose intensity. This, of course, is data from one light fixture only, and one set of bulbs only, so it may not be typical for all 55 watt PC bulbs.

It certainly does indicate that those who advocate replacing these bulbs in less than a year are not getting as much life from their bulbs as should be possible.

If all 55 watt PC bulbs lose 25% of their intensity during the first couple of months, that means the maximum light intensity we see is right after we first set up a new tank, with a new light fixture and new bulbs. Unfortunately, this corresponds with when the plant mass is lowest, the tank is least stable, the CO2 is probably still being adjusted to a good value, the water circulation is probably still being adjusted, etc. No wonder newly set up tanks can run into algae problems so soon.

More data will be needed to be sure this one set of data is typical, but I find this interesting.

 

[SuperColey1]

I think the 1 year rule is for tubes run on magnetic ballasts where they 'flicker start'

The tubes I just changed over (although not PAR tested) were an 18W T8 and a 30W T5HO.

Both were run from electronic ballasts and they were 25 months and 17 months old when changed.

They both looked fine before I swapped them for the LEDs too so I think they would've been fine for a bit longer

AC

 

[VaughnH]

T5 bulbs have the reputation for lasting longer than the 55 watt PC bulbs, but I'm not sure where the reputation came from.

 

[Tom Barr]

I posted several comments that add to Vaughn's post on our local plant club forum.

1. Think about what folks assume about lighting: 90% or more of the intensity is retained, this is assumed and many think that's what happens no matter what with PC/T5 bulbs, as you can see, at least with this batch or data, this does not occur. I'd suspect in many cases this might be true.

2. Such cases show the importance of actually measuring bulbs over time, you need not test often, bulb to bulb differences and maybe you just got a bad one etc can also apply.

3. By testing the bulbs, you can catch things like this and not assume that your light is always the same or similar to everyone else's or that my X watt/gal over a tank is the same, or why doesn't that corn work and grow plant's as well etc.

4. The ends of bulbs are noticeably dimmer than centers.

5. Think about a new hood/bulb in the start when an aquarist buys a tank and starts a new tank: this is the worst case, lots of light/low plant biomass,/no bacteria, later moderate light, and then much later, low light.
How does this influence CO2 and nutrient uptake?

It's better to have the reverse scenario.

So folks get algae and then try a bunch of things, not measuring light, then it just happens and they find the "balance", thinking it's all nutrients, maybe CO2........

You really need to measure all three to say much.
Then you can compare.

But measuring CO2 well is still very tough and a gaping hole.

Regards,
Tom Barr

 

[paludarium]

T5 bulbs have the reputation for lasting longer than the 55 watt PC bulbs, but I'm not sure where the reputation came from.

Hi,

I use the data in this site for T5/T8 bulbs lifespans reference. Lebensdauer von Leuchtstofflampen However, the measurements were based on lumen but not PAR. I'm not sure if PAR intensity decrease is propotional to lumen.

Regards,
Erich

 

[Tom Barr]

Bulbs may work differently with different use, different ballast etc.
So it might be less due to the bulb itself.

Ideal controlled conditions are good for comparison however. That assumes this was done for the data. Problem is, many assume that their tanks and set up is the same. Perhaps 70% of the time it is. But maybe not.

Point is, we assume things and the assumptions have risk.
So the real question is how much, can we measure and test in situ etc.
Then you confirm, not assume.

Regards,
Tom Barr