Cheap T5HO "Plant" bulbs and longevity
 

There has been a couple discussion about different T5 HO bulbs. With T5, the bulb choice are still somewhat limited (unlike T8 or T12). There are some specialty bulbs, but they are expensive. This spring I found a cheap source of plant bulbs (the purplish, gro-lux type). It is from TopDogSellers in ebay (I think the name of the company is GobiiDirect). 2' 24W bulbs are $26 + $12 shipping for 4, and 4' 54W bulbs are $34 + $20 shipping for 4 bulbs. I think the shipping is a bit expensive, but if you order a lot of bulbs in one shot, you might save some. It is still cheaper than some of the plant bulbs you can get from Pet/aquarium Shop.

It is marked as Odyssea Plant bulb.

I wasn't sure about the quality, so I took some simple measurements. I used 2' 24W bulbs. The fixture is Hydrofarm FLT-24, but used only 1 bulb per fixture. Room temp was 66F. Measurement is at the middle, 1 foot from the bulb.

Brand new bulbs:
The 6400K bulb was AgroBrite 6400K.

columns:
PPFD: photosynthetic photon flux density in micromoles/m^2/s, measured by old Li-Cor Quantum sensor (not calibrated recently).
fc.1: foot-candles measured by Gossen Ultra Pro (calibrated, but the spectral response curve deviates from CIE luminosity function).
fc.2: foot-candles measured by a cheap LX-1330B meter (not calibrated, but fairly new, the manual shows a nice spectral response curve, but not sure if it is the true spec.)
watt: this is measured by Kill-a-watt. Since I'm putting only 1 bulb in the 4-bulb fixture, this energy usage is quite a bit of overestimation. Indeed, if you put 4 bulbs, it uses 72.6 watt (not 30wattx4).

PPFD and PPFD/watt columns are the most relevant data for plants. So the plant bulbs give 40% more PPFD per bulb and 23% more PPFD for a given watt. PAR (PPFD) doesn't put weight for red light (which is a bit more efficient for photosynthesis than green light), and it counts the number of photons in 400-700nm range. 6400K contains quite a bit of green (compared to plant bulbs), so the advantage of the plant bulb here is an under estimation.

I have only measured 1 bulb of each type, so I can't say too much, but the cheap plant bulb seems to be pretty good.

Longevity of T5HO.

According to some web site, T5 and T5HO seem to have a bit better longevity (i.e. the output doesn't decline as fast as T8). A couple sites about the lumen maintenance curve can be found: here 1 and here 2. However, when I measured my older bulbs, the output decline seems to be pretty significant.

2 year old AgroBrite 6400K had only 57% output in PAR compared to the brand-new bulb (and 61% in fc).

About 5 months old Odyssea Plant had 70% in PAR (79% in fc).

About 3 months old Odyssea Plant had 87% in PAR and in fc.

The decline in output seems to be much more than I expected. I used to think T5HO should be replaced every two years, but now I think I have to replace them much more frequently. I wonder why there is such a big difference in the reported lumen maintenance vs my measurement. It's possible that since I put the fixture directly on top of acrylic enclosure and the bulbs have shorter life due to the heat. Any ideas?

Inverse square law.
The inverse square law states that the light intensity should decrease to 1/4 if you increase the distance twice. But since T5HO is not a point light source, the reduction of light with distance is slightly different.

The fixture with 4 bulbs of T5HO gives following fc at several distances:
1' 970fc
2' 336fc
4' 93fc
So at 4', it gives about 1/10 instead of 1/16 (=1/4 * 1/4).

Ray has a more detailed info.

Look at the zoo med flora sun t5 ho. Their not a bad price.
I was also looking at the
Wave point Ultra Growth wave (ultra Cola) cost more but has a great color spectrum, blue and red.
I run 3 t5 on each self, I'm going to try 1 wave point Ultra grow in the middle.
You really should change the bulbs every year. Even if it still has the intensity you never know about the spectral shift as the bulb ages.

Why not use WarmWhite or Daylight T5 purchased from a hardware store? Wouldn't these be significantly less expensive to purchase?

4ft, 54 watt bulbs are $3-$6 (before shipping) here:
lamps / bulbs t5 and t5ho fluorescent 54 watt products on sale from Warehouse-Lighting.com

https://www.1000bulbs.com/category/f...nt-tubes-6500k

Brand name bulbs like GE or Sylvania might perform better.

https://www.1000bulbs.com/pdf/ge-46763-specs.pdf

Great info. The trouble with David's source above is you have to by cases of 40 bulbs.

I must admit to being confused because pricing is all over the place and nobody wants to feel ripped off especially if the T5's are all basically the same and we just don't know it.
However I wonder if the specified number of lit hours provided is any indication ? These are quite costly
T5 Bulb | T5 Replacement Bulb | Gardener's Supply
but state only for 10,000 hours. Does that mean that as a result of not lasting as long, they are more effective and don't have to be replaced until that 10,000hr limit approaches ? Or - can you buy the '24,000hr' lights and just replace them more often to get the same efficacy ?

Naoki
What bulbs did you end up going with?

---------- Post added at 09:57 PM ---------- Previous post was at 09:04 PM ----------

The bulbs only last about a year 4500 hours or so.
That's when they need to be replaced. Par drops spectral shift what ever happens. When they say 2 years or 10000 hours that's the life of the bulb before it fails completely. Any specialty bulb for growing plants reef tanks ect. They will say 4500 hours or year. That's their market so they will state it. General lighting bulbs will say 2 years or 10000 hours. What we are using them for they should be replaced every year.
It is the life support of our plants for use growing in doors.
No one questions spending 20- 30 on fertilizer. You need quality light.
One of best 6500k bulb is the GE starcoat from what I've read, very high par.
The hotter the bulb the shorter lifespan. If you have a fan blowing on them they will last longer.
Hope this helps.

I've forgotten about this thread...

Philip, I'm still using Odyssea Plant bulb for 2' (24W) since I ordered extra (to minimize shipping cost). The ones you mentioned is pricier (well at least for me who has to get them shipped). For 4' (which the shipping cost is even higher), I'm just using the cheapest one from HomeDepot. 1000bulbs etc, which David recommended, has pretty high shipping cost for me.

I agree with you that light (carbon) is much more important than fertilizers for us, artificial light growers. And the efficiency of light make a big difference in how much we are spending money for the hobby.

I did make a bit of space between the bulbs and the enclosure for better cooling. I'm following the decay of T5HO from the fresh bulb in a different fixture (trying to measure once a month), but it does seem to decay rather quickly. If I know the decay curve better, I can see whether replacing the cheap ones quickly or getting the fancier ones less frequently. But I don't have many fluorescent light left, and after I use up the extra bulbs, I probably won't use florescent light any more.

Orchidsarefun, I don't know the answer to the question.