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

[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.

[Ron99]

Well you make a few assumptions in your financial analysis. I do believe 10 years is a reasonable lifespan even though you disagree. Since nobody has had a decent LED fixture for 10 years yet we can't really tell. So let's look at the 6 year point as an example. The costs you laid out for the LEDs was $2000 purchase price with $110 per year in running costs for a total after 6 years of $2660. The MH was $1000 to purchase + $220 per year in electricity and $140 per year in bulbs for a total of $3160. That is also assuming you don't need to buy and run a chiller which will add a fair bit to the MH costs.

You have also made the assumption that in 6 years if the LEDs need replacing then a fixture will again be $2000 but the costs are likely to come down dramatically by then and you will get a comparable setup for far less money. But you might also be able to simply replace the LEDs by that point and the costs for comparable emitters would likely be less than $200 for say 80 LEDs by that time. There is a big push to incorporate LED technology into mainstream lighting so in 6 years the economies of scale will bring the prices way down. I can already buy generic 3W LEDs with maybe 70% the performance of Crees for $1.50 each (I have some I plan to test soon). In 6 years they will exceed the performance of the current Cree LEDs at or below that cost. You are also assuming that users of MH or florescent lighting use the same fixtures indefinitely. I venture that most people in this hobby change their fixtures at least every 5 or 6 years. Of course some won't and you will find the outliers who have been using the same MH setup for 10 or 15 years but they would be the exception rather than the rule.

I also think it is a false to assume that repairing an LED fixture is more difficult or costly than repairing a faulty MH or T5 fixture. It may or may not be depending on what fails. Replacing an LED is not any more difficult then replacing an end cap or moonlight and replacing a driver should not be any harder then replacing a ballast. If you would feel comfortable repairing a MH or T5 fixture you should be able to do the same with an LED one. If you aren't comfortable then it has to go out for repairs no matter what lighting technology it uses. And MH and florescent ballasts aren't cheap to replace and they do fail over time. So we should leave the failure/repair estimates out of the analysis because there are so many variables there.