LED idea

[theatrus]

I have 6 BlueAcro Mega4Z 20KBlue Pro pucks on my 150g reef (along with 4 x 80W T5s). Because I clumsily broke many of the diffusers (even after Theatrus kindly replaced a bunch of them), I have about 3 pucks with them and 3 without. I have to say that I do not see any sort of disco ball effect without the diffuser, but with them, the light is a bit softer (although I have not measured PAR). I like them a lot.

The Luxeon Z are more immune to this. The C get crazy looking quickly - those secondary optics make a big difference.

 

[shred5]

Been saying this for years.
I work in the lighting industry and this is how it is done with allot of led fixtures.
Indirect will defiantly spread the light and help with self shading.
You would loose a little light for sure as it bounces back at the light source.

 

[jsker]

Interesting concept. wouldn't there be a dead spot in the center?

 

[shred5]

Interesting concept. wouldn't there be a dead spot in the center?

Some of the light is direct and some of it is indirect..

 

[Sleepydoc]

The key thing to remember here is that a MH light emits light 360º around the bulb, so you need a reflector to capture the other 300º of light that would otherwise miss your tank. Unlike MH's, LED's emit light in only one direction. You can alter the spread with a lens, but there is no light being emitted upwards.

Shining the light upwards and using a reflector may alter the spread, but will invariably decrease the intensity; both because of the increased distance and also because of the less than perfect reflectivity of the reflector. There is the possibility of altered spectrum, depending the spectral reflectivity of the reflector as well.

@Lukas75 raises a good point as well about the heat; LEDs get their big heat advantage both form the fact that they don't generate much infrared spectrum radiation, and that the majority of the heat is from the power supply and directed upwards, away from the tank.

Edit: just noticed that @Skydvr said essentially the same thing in his post. I agree!

 

[oreo54]

Shining the light upwards and using a reflector may alter the spread, but will invariably decrease the intensity; both because of the increased distance and also because of the less than perfect reflectivity of the reflector. There is the possibility of altered spectrum, depending the spectral reflectivity of the reflector as well.

Funny, that is never really considered though aluminum has some wavelengths it absorbs more than others..Fortunately not so much in the visible spectrum.well its even..
IF you want to do a mixing chamber and then basically focus it your reflector should be coated w/ a high content Barium Sulfate paint..

https://www.labsphere.com/site/assets/files/1831/pb-13026_rev01.pdf

Though I doubt if you would get color shifts w/ either..

Though really nit picking here.. more for curiosity, since you mentioned color..
Point is aluminum does absorb some light..
Barium does have its own weaknesses.. like yellowing over time ..

 

[Sleepydoc]

Thanks for the info, Oreo. Aluminum can oxidize which would obviously alter the reflectivity. I wonder if the manufacturers coat the reflectors with any sort of reflective coating? I assume they would verify the optical characteristics of any such coating, but that’s also something I can see differing between various manufacturers, especially between cheaper and higher end ones. Also, are the reflectors all polished aluminum, or are they made of other materials? Again, it’s not something you think a lot about - you open the box and see a shiny reflector and you assume that one kind of shiny is the same as another kind of shiny.

 

[oreo54]

Doesn't matter .. aluminum has its "native "absorption..Highly polished or not (exaggerates scatter) highly collimated or not.
You lose light over "other material"... ;)
sintered teflon absorbs about 2%
IF I understand this right Al "absorbs" about 8% of the light in the visible spectrum...
after that losing spectrum is dependent on "other things"...
dirt.. geometry.. oxidation ect..
slightly absorbs more red than blue..

 

[theatrus]

Aluminum is likely bright dipped and clear anodize. This takes a harder alloy (not 6061).

https://www.pioneermetal.com/anodizing-finishes/bright-dip/bright-dip

You might also end up with a Cerakote