# What tubes?



## StevenA (23 Feb 2008)

Hi all, i have a 100cm overtank luminaire that i wish to replace the tubes in. It has 3x 39w T5's in it, and i think they are standard daylight tubes. I want to promote better plant growth, so should i buy 3 Grolux tubes or 2 Grolux and a new daylight tube or another combination? The site i use in the UK is http://www.lampspecs.co.uk/


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## ceg4048 (23 Feb 2008)

Hi,
     There is no correlation between the Kelvin temperature of the bulbs and growth rates of plants. The bulbs you have will grow your plants exactly the same as any Grolux tubes. Plant growth rates are correlated to light intensity, CO2 concentration and nutrient availability. The plants adapt to the frequency provided, so that Grolux doesn't grow plants any better than cool white.

Color temperature should be used based on what color you like looking at, that's all. See JamesC's threads on the various color effects: http://www.ukaps.org/forum/viewtopic.php?t=555 http://www.ukaps.org/forum/viewtopic.php?t=523

Cheers,


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## StevenA (23 Feb 2008)

I've had the tubes for about a year now, so should they be replaced anyway?


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## ceg4048 (23 Feb 2008)

Well, I see a lot of posts in various websites about how bulbs should be replaced after a year, but I've never been convinced. If I can see the light why can't the plants see it?  I mean, it's not as if there is some invisible secret energy being produced by the bulbs only when they are new. If there is some intensity falloff or frequency shift of the bulbs as they age the plants adjust their pigment allocation or chlorophyll efficiency to account for the color shift or drop in intensity. I replace my bulbs only when they disintegrate or when they don't glow anymore, but then again I'm a cheapskate.   If the lights come on when they are supposed to, and if your plants still grow then I can't see any good reason to throw Â£14.99  away. JamesC may have a better take on this though.

Cheers,


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## JamesC (23 Feb 2008)

Without a light meter it's very hard to tell how light levels drop with time. With T8's I always replaced them after nine months only because the ends got quite black. May be able to last a bit longer. When compared with a newish tube they did look quite a bit dimmer to me. A new tube when first used will be very bright for the first week or two and dim quite quickly. From then on it will dim a lot slower.

T5's are supposed to last longer but I'll probably change them each year. They will actually last a few years until they fail. A lot of it I think is up to you and your budget at the end of the day.  Some people replace them as quickly as every six months while others keep them going until they fail.

James


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## .jaap. (23 Feb 2008)

Mercury vapor in the tube creates UV light, which strikes the phosphor coating on the inside of the tube. The phosphor absorbes the UV and converts the energy in the UV into the visible light that you see.

Over time, the mercury vapor is absorbed by the coating, and the lamp will loose much of it's brightness.

Some tubes have a protective layer on the coating that will prevent the mercury absorbtion. These lamps will loose only a small amount of their original brightness over time.

For growing plants there are two important factors: How much light is produced (lumen) and how efficient is that light when it is used by the plants:

Brand            Type	 Efficiency
Philips TL D	927	240
Philips TL D	930	230
Philips TL D	940	220
Philips TL D	950	220
Philips TL D	830	195
Philips TL D	840	195
Osram	21	195
Osram	31	195
Sylvania	CWX 184	195
Sylvania	WWX 183	195
Philips TL D	827	180
Osram	41	180
Philips TL D	865	170
Philips TL D	33	160
Osram	20	160
Sylvania	CW	160
Philips TL D	54	140
Osram	10	140
Sylvania	D	140
Sylvania	CWX	135
Duro Test	True lite powertwist	135
Sylvania	IF	130
Sylvania	WWX	130
Duro Test	True lite	130
Osram	19	120
Osram	flora	110
Sylvania	Grolux	100


Sorry for the layout.

From this table you can see that Philips 927 is 2.4 times as efficient as Sylvania grolux. So you can use either 100 Watt of Philips, or 240 Watt of grolux to get the same production of plant mass.

In Holland the Philips 830 and 840 tubes are very popular for aquarium use. These tubes also have the protective coating to avoid mercury vapor loss, so they do not loose much of their initial brightness. Use them until they are dead. The same goes for the 9xx series in T5 from Philips, which give even better color rendering. The 830 and 840 types are very affordable, only a fraction of what you may have to shell out for a special 'aquarium' lamp (that you have to replace after a year or so).


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## JamesC (23 Feb 2008)

Just like to pick up on a couple of points which I don't agree with



			
				.jaap. said:
			
		

> For growing plants there are two important factors: How much light is produced (lumen)
> 
> 
> From this table you can see that Philips 927 is 2.4 times as efficient as Sylvania grolux. So you can use either 100 Watt of Philips, or 240 Watt of grolux to get the same production of plant mass.



Lumens is only a measurement of the yellow/green part of the spectrum which our eyes are most sensitive to. It does not measure the red and blue spectrums which are mostly used by plants.

The reason Grolux's have a rubbish lumen figure is that they produce almost no yellow/green light but loads of red and blue light. A much better way of measuring light output for plants rather than offices is to use PAR (Photosynthesis Action Spectrum) or even better PUR (Photosynthetic Usable Radiation). These give the light output across the whole photosynthesis range.

Using these figures Grolux's score very highly, higher than most other tubes, and this is the reason why they are so good at growing plants. 

James


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## .jaap. (23 Feb 2008)

You have a strange way of quoting. What I said is: For growing plants there are two important factors: How much light is produced (lumen) and how efficient is that light when it is used by the plants:


The tabel does not mention lumen   :idea:   but growth efficiency.


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## JamesC (23 Feb 2008)

Er, you started the sentence by stating for growing plants and then mentioned how much light produced in lumens.



			
				.jaap. said:
			
		

> For growing plants there are two important factors: How much light is produced (lumen) and how efficient is that light when it is used by the plants:



How is that eficiency measured? All the figures I've ever seen using PAR or PUR measurements put Grolux's fairly high in the list, but using Lumens they come at the bottom. I did presume that the eficiency figures you quoted were in Lumens as the Grolux's were at the bottom but it'd be interesting to see how these eficiency figures were arrived at.

James


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