Yea I was worried about the height of the tank with the LEDs. The main reason for the swap apart from the running costs is that my current setup leaves a dark gap at the edges of the aquarium so I have had to place 2 LED strip lights there that I had before. I also prefer the look of the LEDs with the shimmer you get on the water.
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The biggest 'disadvantage' with LED technology is the 'lack' of standardisation. LEDs vary wildly in performance and application.
So you need to cut through the marketing c**p ("Patented Dense Matrix LED™ technology" - yes, that Kessil site is a marketing wonderland) and focus on the fundamentals. In a semblance of order, I would look at - actual output (in lumens), effectiveness, efficiency and aesthetics. I take controllability as a given for LEDs (and is still the main reason I use them rather than fluorescents) - but many low end suppliers still don't provide even basic dimming functionality.
Output
I'm guessing your current 4 * 39w T5s will be producing around 12000 lumens of output. You'll be losing a little of that to reflector inefficiency - but that applies to virtually any reflector/lens based system - be it LED or fluorescent - so just ignore it.
Coincidentally extrapolating up from one of my tanks, I get that same figure - so I would suggest that as the starting point and maybe increase to 15000 or more for extra headroom. Of course, if you go LED, you can adjust down from there to any level you like.
So you'd need roughly 3 of the Beamswork units you mentioned before to get to that level. Feasible but probably not the best solution
Effectiveness
By this I mean the ability to direct those 12-15000 lumens of light to where they're needed.
Most 'regular' LED fixtures have a spread of about 120-130degrees. This 'encourages' people to place those fixture close to the surface of the water to minimise light spillage and maximise the amount of light entering the water. This gives a good spread of light throughout the tank, including upper and lower levels - but that spread also means you lose more light from the sides of the tank.
(As an aside, anyone with one of these units will confirm that the spread is actually closer to 180degrees but the light output drops off towards the extremes - as far as I can tell the manufacturers calculate the reported spread based on the angle at which the light output has dropped to 50% of its peak.)
Other units, such as the Kessils and Orphek, use lenses to focus that light. This is typically either 60 or 90 degrees for freshwater/planted tanks. These have the advantage of minimising light loss/spillage (although again, no lens is 100% efficient) and providing a concentrated cone of light that penetrates well. So minimal light loss but at the expense of poor light spread - worse at the surface where there will be significant areas with poor coverage and still not ideal at the bottom, where you will have circles of light, areas of dark - and a limited ability to remedy that with multiple sources.
You also need to differentiate between the Kessil type units with multiple LEDs focused into a cone (i.e. like a spotlight) and other units (Orphek?) that use individual lenses for each LED - spread is less of an issue for the latter types.
So you need to take a view on spread versus penetration (yes - that's a bit of a simplification!).
Efficiency
As Ian has already mentioned, you can easily buy low end LEDs that are less efficient than fluorescent technology. Your current T5s consume 156watts at about 75 lumens per watt - and the 54w tubes Ian mentioned can drive that up to over 90 lumens per watt. The best LEDs currently available on the market will easily give you 150 lumens per watt. I could build you a system that would give you the equivalent 12000 lumens for 80watts - and it's always worth remembering that's not just a saving in power costs, the flipside is a marked reduction in heat generated - which can be an issue for many people.
As a gross generalisation, the lower powered, individual LEDs are less efficient and LEDs that run at up to 3 watts each will be more efficient. (Many top end LEDs can be run at higher power than this but they run less efficiently and are harder to cool). If it isn't explicitly stated, you can usually deduce from the specs what type of LEDs any unit is using.
Aesthetics
Mostly just focusing on the shimmer effect that you like. It's unlikely a couple of hundred low power LEDs are going to give you that effect as there are so many small light points. For better shimmer, think smaller number of higher powered LEDs or the tight cone provided by something like a Kessil unit.
I don't have much interest in light spectrum - I think it's a huge red herring. Pick cool white, neutral white or warm white and be done with it
and of course - do you need the great looks of a Kessil unit (and the cost it entails) when it's going to be hidden under an oak hood?
All told, I'm not entirely sure if any of that will help.. but food for thought perhaps..
Regards, Mark
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