L.E.D. vs HALIDE/T5/VHO

[Ron99]

Originally Posted by sphelps

Bulbs with a lower K rating typically produce higher PAR because, as you said, it's related to the amount of useful radiation (more of it in lower spectrum bulbs). So if PAR and spectrum wear where directly tied together, as you stated, then with certain bulbs you would see an increase in PAR as the spectrum shifts in the lower K direction. We of course know this isn't the case and the article I linked suggests that the change in par and spectrum overtime are independent not dependent. The decrease in PAR is related more to the decrease in intensity not the shift in spectrum. Of course certain bulbs preform differently so some may be more effected by the spectrum shift but avoiding such bulbs is pretty easy these days with all the information we now have.

So just because an LED doesn't suffer the same spectrum shift as other bulbs doesn't mean the PAR rating will be unaffected, it simply means you won't notice a change in color overtime, only intensity.

It's actually more complicated then that. The spectral shift of bulbs actually makes a big difference in PAR. First have a look at this figure that shows the peak absorption wavelengths for chlorophyll:



You can see that chlorophyll likes blue and red but not much in between. Now here is a good article on the spectral output of various MH lamps:

http://www.personal.psu.edu/sbj4/aqu...omparison.html

Here is the output of a 10,000K Ushio bulb as an example:



So as that big blue peak not only decreases but shifts over the the right you get less real useable PAR since the green part of the spectrum is less efficient then the blue and red in terms of photosynthesis. The situation is probably even worse with 14,00K and 20,000L bulbs that have more blue and less red in their spectrum. Here's a 20,000K bulb:



So yes, the lack of spectral shift in LEDs is a big advantage in that you stay in the peak output frequencies for photosynthesis. I imagine the T5s etc. put out similar spectrums as some of the MH lamps so the situation is similar.

[Ron99]

Eugene beat me to it but I had diagrams

[OceanicCorals-Eugene-]

Originally Posted by Ron99

Eugene beat me to it but I had diagrams

your diagram helped explain it better then what i can with words.

[sphelps]

While I applaud your skills of posting diagrams exactly how is posting diagrams of bulbs running with different ballasts relevant to bulb life? I also obtain the skills to post diagrams from articles however I will post ones more relevant to the discussion.

First we can look at the same bulb at 0 months and 17 months:

While the AVERAGE spectrum or CCT will shift in one direction the actual plot does not actually shift but rather decrease in certain areas while increasing in others resulting in a new CCT. Typically the intensity of the blue will decrease but depending on the ballast you use the other areas of the spectrum will actually increase maintaining your total PAR but changing the overall color of the bulb.

Here we can see PAR readings of the same type of bulb over time

Clearly shown is a steady par reading but a decrease in CCT

So we can pretty clearly conclude

If the change in spectral output is not a big concern, these lamps can be used for much longer periods of time

So yes the CCT of halide bulbs will change from a result of a change in intensity of different wavelengths but this doesn't mean lower par. Results will vary for different bulbs but proper selection will prevent overly negative results.

The reason you don't see the change in CCT with LEDs is simple. The spectrum is much more defined and concentrated over a smaller area. The intensity simply decreases over time and since it lacks the other wavelengths there is no increase in other sections keeping CCT constant.


So once again the change in PAR is more directly connected to the change of intensity of each wavelength that makes up the Photosynthetically Active Radiation (PAR) and not necessarily the overall change of the Correlated Color Temperature (CCT).

Also there is more to PAR than just red and blue

Photosynthetically Usable Radiation, or PUR, is that portion of Photosynthetically Active Radiation (PAR) that is actually absorbed by photosynthetic pigments. Photopigments found in zooxanthellae of corals include chlorophyll a, chlorophyll c2 and peridinin. Typically, these pigments as a group absorb violet, blue and portions of the green wavelengths, as well as most red wavelengths. Since zooxanthellae can 'tweak' pigment ratios in response to light intensity and/or spectrum (within reason!), we can only generalize the wavelengths associated with PUR - for our purposes, PUR for corals and other animals containing zooxanthellae includes bandwidths of 400-550 nm (violet, blue and some green) and 620-700 nm (red).

http://www.advancedaquarist.com/2009/3/review
http://www.advancedaquarist.com/2008/7/aafeature1
http://www.advancedaquarist.com/2006/8/review2

[OceanicCorals-Eugene-]

Originally Posted by sphelps

While I applaud your skills of posting diagrams exactly how is posting diagrams of bulbs running with different ballasts relevant to bulb life? I also obtain the skills to post diagrams from articles however I will post ones more relevant to the discussion.

First we can look at the same bulb at 0 months and 17 months:

While the AVERAGE spectrum or CCT will shift in one direction the actual plot does not actually shift but rather decrease in certain areas while increasing in others resulting in a new CCT. Typically the intensity of the blue will decrease but depending on the ballast you use the other areas of the spectrum will actually increase maintaining your total PAR but changing the overall color of the bulb.

Here we can see PAR readings of the same type of bulb over time

Clearly shown is a steady par reading but a decrease in CCT

So we can pretty clearly conclude


So yes the CCT of halide bulbs will change from a result of a change in intensity of different wavelengths but this doesn't mean lower par. Results will vary for different bulbs but proper selection will prevent overly negative results.

The reason you don't see the change in CCT with LEDs is simple. The spectrum is much more defined and concentrated over a smaller area. The intensity simply decreases over time and since it lacks the other wavelengths there is no increase in other sections keeping CCT constant.


So once again the change in PAR is more directly connected to the change of intensity of each wavelength that makes up the Photosynthetically Active Radiation (PAR) and not necessarily the overall change of the Correlated Color Temperature (CCT).

Also there is more to PAR than just red and blue


http://www.advancedaquarist.com/2009/3/review
http://www.advancedaquarist.com/2008/7/aafeature1
http://www.advancedaquarist.com/2006/8/review2

The posting of a graph is not to show different different ballasts used but the spikes in individual ranges.

I'll agree with you that PARs values change according to the change in intensity of different wavelengths but how is that different with a shift in the spectrum? (might just be my way of reading it that i see them as the same). So would you say that the PAR value decrease is correlated to a decrease in intensity and color spectrum shift not intensity alone? now that you've mentioned that its % of intensity drop in certain spectrums.

Its true that theres more to red and blue in PAR but those are the 2 main spectrums that plants/corals utilize. There is a need for green/yellow but the 2 most utilized spetrums are red and blue thats why i only mentioned the 2.

This discussion is interesting!

[sphelps]

Originally Posted by OceanicCorals-Eugene-

So would you say that the PAR value decrease is correlated to a decrease in intensity and color spectrum shift not intensity alone? now that you've mentioned that its % of intensity drop in certain spectrums.

I would say that PAR is obviously related to CCT, different bulbs produce different PAR based on this, but not so much for the change of PAR overtime from bulb wear. A decrease in PAR would be more a result from a decrease in intensity alone as changes in CCT could either increase or decrease PAR or even remain constant.

So I guess to sum up what I'm suggesting is a decrease in par is a result of an overall decrease in intensity while a change in CCT is a result in a shift or varying fluctuation in intensity over different wavelengths. CCT and PAR are not directly related when we're looking at bulb wear.

So when comparing LEDs to halides, LEDs will still suffer from a decrease in intensity and therefore PAR but the rate of reduction of intensity in LEDs is less than halides. The narrow spectrum in LEDs makes the change in CCT is basically unnoticeable while halides suffer greater changes due to the more broad spectrum. So LEDs obviously last longer but halides are cheaper and easier to replace and by selecting bulbs with a more concentrated spectrum in the right areas you can extend you bulb life dramatically.

[Ron99]

Eugene is correct. I showed those charts to show how the bulbs we choose for reef applications spike in the same wavelengths as the most efficient ones for coral photosynthesis.

PAR meters measure all light between 400nm and 700nm. However, 500 to 600nm light does not produce as much photosynthesis as light around 450nm or 650nm to 700 nm. So while overall PAR may seem to stay the same or drop somewhat overall PUR (Photosynthetically Usable Radiation as shown in some of the articles you linked to) may drop more than PAR since the decrease in blue is probably more than the decrease in the green to red part of the spectrum. So we should probably look more at PUR than PAR but few people have spectrophotometers that can do the more complex analysis. What is intersting is that if you measure PAR of a cool white LED and compare to a blue LED, they put out very similar PAR numbers. I would be really interested to see what a PAR meter measures for a green LED of similar wattage. I suspect that PAR would be very close to the others but that's not PUR and corals would not do well under pure green LEDs.

MH and florescent bulbs degrade relatively quickly (within 1 to possibly 2 years with the better bulbs) such that PUR decreases as the overall spectral output changes (or shifts depending on your frame of reference) to be more warm. It is fairy well accepted that nuisance algae grow better at warmer colour temperatures and old bulbs can promote their growth, as I have seen first hand with my old T5 bulbs. If things did not change in that way why change bulbs so often? So to summarize, blue decreases a fair bit but green to red increases somewhat so the loss of blue in the PAR is offset somewhat by the increase in green and red. But that does not mean PUR stays the same, it will decrease and the corals will not be photosynthesizing as efficiently.

I still contend that LEDs have a great advantage. A 30% decrease in 50,000 hours means that with a 10 hour a day lighting schedule you could theoretically get 13.5 years of use and PUR will drop 30% in that time. But the CCT will stay the same and you should not have problems with nuisance algae as the LEDs degrade. Realistically, how often do you change your MH bulbs and what do they cost each time? My T5s would realistically last no more than a year and replacement costs were $250 to $300. Let's say the LEDs last 10 years then I am saving $2500 to $3000 in bulb costs. Then add the electricity savings as well as the reduced likelihood of needing a chiller (more an issue with MH than T5) along with the stability of the CCT and LEDs look pretty good.

This whole debate reminds me of the T5s vs. Metal Halide debate. There was great resistance to T5s with people strongly believing that you could not have a thriving SPS tank under T5s and that T5s were inferior to MH (heck, that debate is probably still ongoing). But we now know that is not the case. The same accusations are being leveled at LEDs but I do believe that time will show that LEDs are a very good option for lighting reef tanks.

[sphelps]

Well first realistically you won't get 13.5 or 10 years out of your LEDs as we already agreed. The same unrealistic numbers are given to both halides and T5s and previously discussed. Second how does your bulb and energy savings compare if you have to replace your fixture every six years compared to simply changing bulbs every year?

The other advantage to T5s that people tend to forget is the ability to setup a kind of bulb replacement rotation. Basically only replacing 2 out of 8 bulbs every six months, every time replacing a different set. This keeps your light levels more consistent eliminating the need to lift and lower fixtures and shocking corals. It also means you're only placing half your bulbs every year which saves you significant money in bulb changes.

The most common argument to go with LEDs is to actually save money in the long run which I think you LED guys should stop using and push more on the lower heat and more defined spectrum (if that really is an advantage).

If you're LED fixture costs $2000 and lasts say 6 years and uses around 250W which means it'll cost around $110 per year for power. If you have to replace your fixture every six years then after 10 years (if you keep it that long) it'll have cost you around $5100.

Now if you compare that to say a 500W halide system which can be purchased for around $1000 (equal quality) and will cost around $220 per year to run for power and around $140 per year for bulbs. After 10 years (again if you keep it that long) that adds up to $4600.

Both realistically are comparable in basic cost however neither include premature failure which is possible for both options however the halide system would offer a cheaper fix. Also after 10 years you only have 2 years left on your second LED fixture and if at some point you decided to sell your fixture for whatever reason the halide system will no doubt return a larger percentage of your investment. And I know that you can argue that you build your own fixture so it was cheaper and you can replace LEDs easily and blah blah blah but what about the rest of us who don't want to or can't build such things, I call this the real world as at least 90% of people in the hobby don't want to build there own light fixture.

[Snaz]

Originally Posted by Ron99

It's actually more complicated then that. The spectral shift of bulbs actually makes a big difference in PAR. First have a look at this figure that shows the peak absorption wavelengths for chlorophyll:

Nice summary with good data and purty pictures. LED FTW