LED vs T5 Efficiency

[Sangheili]

So one of the sticking points I usually hear about LEDs is that they use way less power then T5's. Having both a 300w LED fixture on my frag tank and an ATI 4 bulb 48" fixture on my display - and a PAR meter, I just flatly don't see it.

And now I went in search of data/research and the first thing i looked up is the lumen output of normal white light sources.

T5: 5000 for 54w - 93 lumens per watt

http://www.gelighting.com/LightingW...LongLast_Lamps_Data_sheet_EN_tcm181-12831.pdf

LED: 456 for 5w - 91 lumen per watt

Cree Components XLamp XT-E White LEDs

Granted these are both likely not "best of breed" light sources but I find the comparison interesting. Personally I feel like I am getting 2x the light from of my T5 setup as I do from my LED setup. The LEDs have optics and hang pretty much the same height as my T5 - and the tanks are very similar. The PAR is roughly similar between the two but the LED fixture covers only about half of the tank vs the T5 fixture covering 100%. And don't forget 300w for the LED vs roughly 200w for the T5. Again none of this is scientific, as I have not compared real energy usage with a watt meter.

Am I missing something here, or are T5s just as energy efficient as LEDs?


(And yes I know T5s have replacement bulb cost and all - please this is not a comparison of T5 vs LED - only a discussion of energy use)

 

[redfishbluefish]

I've seen similar studies comparing household LED's to household compact fluorescents where lumens per watt were very similar.....similar to what you found.....so I'm not surprised by your numbers....they make sense. However, with our tanks, it's PAR and PUR that are critical, and I've never seen anything that compares these all important parameters to wattage.


I can only tell you that I've replaced 6 T5's overdriven by IceCap ballasts (supposedly 480W) with two 120W LED units (240W). Now I never measured PAR, but stuff appeared to grew similarly under either light choice.

 

[hart24601]

Really we want to see PUR/watt, but PAR/watt is good enough. I have not done side by side tests since I don't have any 6 or 8 bulb t5 fixtures, but also remember to not just go by the watt ratings for LEDs if not running them at 100%, best to use something like apex to see the current draw of both. Also the LEDs become more efficient if run lower as most people do. Back when I had my 65 I ran 200w according to apex and had even 500 PAR on rock 3/4 up, 300-400 mid level and 200+ on the sand. They were not particularly efficient reefbreeder LEDs, but I have not seen anything that can make those levels at that wattage.

 

[Sangheili]

My problem with using PAR as a measurement is PAR does not take into account the total light emitted from the light source. It is my understanding that when these companies show a lumen rating, they are sticking the bulb in essentially a spherical chamber and measuring all light that comes out of it from every angle. PAR (at least with consumer meters we use in our tanks) is more of a point measurement.

I would love to see Total PAR measurements from various lighting technologies using a similar method to the Lumen measurement. Measuring the PAR at a couple points in the tank below the fixture gives a rough idea of light coverage and intensity but not nearly the same thing as measuring the total output from the light source.

 

[hart24601]

PAR is down to UV which we can't see and don't want (400nm) and up through red pretty well. I don't think the apogee reads the far deep reds well, but after that is infrared light so in general PAR meters give a pretty good reading of light output. After applying correction factors for the numbers apogee doesn't read well it cover most of the visible light spectrum aside from really deep near infrared so PAR seems pretty good to me.

 

[Sangheili]

PAR is down to UV which we can't see and don't want (400nm) and up through red pretty well. I don't think the apogee reads the far deep reds well, but after that is infrared light so in general PAR meters give a pretty good reading of light output. After applying correction factors for the numbers apogee doesn't read well it cover most of the visible light spectrum aside from really deep near infrared so PAR seems pretty good to me.

The problem isnt measuring spectrum. The problem is capturing all of the light that is output. The PAR meter only senses the light which reaches it, not the light spread all around it. Its like measuring intensity vs quantity.

 

[hart24601]

Sure but generally for our purposes those bulbs have reflectors that direct the light down into the tank with varying losses so to me a PAR reading is a good enough for me and I think better reflects, no pun intended, the light our animals receive. I am not concerned with reflector issues or light spilling out of the tank. I don't want to waste the power to do that, I want to direct that energy on my animals. The best would be to move the sensor over the entire tank surfaces and computer map the PAR reading, but making PAR map with 20 or so points I fee is a good indication of watts spent vs light to the coral.

 

[Sangheili]

Sure but generally for our purposes those bulbs have reflectors that direct the light down into the tank with varying losses so to me a PAR reading is a good enough for me and I think better reflects, no pun intended, the light our animals receive. I am not concerned with reflector issues or light spilling out of the tank. I don't want to waste the power to do that, I want to direct that energy on my animals. The best would be to move the sensor over the entire tank surfaces and computer map the PAR reading, but making PAR map with 20 or so points I fee is a good indication of watts spent vs light to the coral.

Well sure thats one way to look at it, but T5 and LED push their light in very different ways. LEDs are a very direct point source light with optics whereas the T5's spread light out much more (being a round long tube). The point of the thread isn't "how much PAR do they put off directly under them" but rather how much light energy do you get over vs the power used. Using PAR measurements directly below the light source would show that LED puts out way more "light" then T5 per watt but that just isn't the case - it's just more focused (which is arguably worse for most coral).

Again the point of this discussion is to try to compare the total light output between the technologies, not the amount of light focused directly below them. Both technologies can use optics and the optics introduce another variable I am trying to avoid in the discussion.

 

[hart24601]

I didn't say the only measure directly under the fixture, but the entire area of the tank. That is the total light the tank gets, you just need lots of par measurements or a computer to create a map as I said already. It's just taking point readings over the surfaces. For our purposes what else matters? The light a tube puts out in a 360 radius isn't important for our purposes as that light has to be directed into the tank. If you don't want to add reflectors into it then as you found t5 can produce similar lumens per watt, but without a fixture most of that will be directed to the sides and above the tank. You already found the info about total light output.

If one wanted to put a single T5 bulb over the tank with no reflector at all, just the naked bulb the total amount of light would be very good per watt, but not much of that is getting into the tank. Put another bulb next to it and that will block some of that light from just having 1 bulb so the total amount of light is not purely additive. Ok, so we then use great individual reflectors for some units, but despite some of those being well designed there is some light loss from being reflected and blocked by itself along with potential light spilling out of the tank. I just don't see why we would want any other type of measurement when now with USB PAR meters being released we should have the ability to map the PAR of every inch or surface the coral could be on. Now a PUR meter would be sweet. Maybe someday.