Cali Kid Corals

Does light power add liinearly??

S

sfsuphysics

Supporting Member
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Asked this over at the useless board, and my post went to the 3rd page after a few hours, so I'll try here.

I'm thinking of swapping out a 250w fixture for a couple 150w fixtures that are simply closer together (plus the DE nature of the pendants gives me room to add in T5 lights as well, I can stagger them being on... etc).

So my question is will those two penetrate just as well as a single bulb? It is a point source, I can't imagine the extinction of the light in the water would somehow occur at a faster rate because it's less wattage. Sure the distribution of energy would be a bit more less spot-lighty simply because there are two sources. But I'm wondering how well it'd work. (plus I'm sure the addition of the T5s will add more than enough light.

Just asking because I need a new ignitor for the m81 ballast, the only place i can find is hellolights, although it's $45, but they got a 10% off deal today july42008 as the coupon code I swore I found one for half that a while back, I sent message to ask for some specs on the thing (to see if it matched up) but never got a response.
Btw anyone know where to find an ignitor?? :D
 
You won't gain any penetration from what I understand Mike. The penetration ability sort of comes from the amount of light it can throw at the water and still make it past the surface layer. The more that makes it, the further deeper it can go. If you add two 175w and get rid of the 250 watt, you'll gain more PAR but loose some penetration power, IMO/IME :D

You can get ignitors at most lighting stores. There is a great one in the City I've been to but I do not recall the name of where it even was (I didn't drive there, some one else did). Let me see what I can find in my links for you :D
 
Hmm guess I'm over simplifying the penetration then, thinking of it simply as a light wave that gets past a surface, a fraction gets reflected that won't depend at all on how bright the source, then whatever is left gets extinguished as it goes down.
 
Mike light will add linearly if they are superimposed. Since they are side by side, they won't, but in close proximity, they will be close to a superposition. When people talk penetration, they are just talking about how much light you can get to a certain depth dictated by its lumenous decay. This touches on Gresham's comment. The surface reflection is a pure percent loss, not a constant, so it scales perfectly well with multi emitters. A bit of "penetration" curiosity is the reflector. Yes a MH is a point source which decays as 1/R^2, but you toss in a reflector and it really breaks down. If you consider all the non reflected light in a point source, yes it decays as 1/r^2. If you take a perfect point source and now consider only the reflections on a perfect parabolla, there is zero decay since the light is now columnated. (well, there is absorption decay, but that is trivial over a few feet). Add those two together and a point source metal halide in a reflector like a lumenarc/bright/max etc or even a spider reflector, will be somewhere between.

So the short answer is, yes, with the same reflectors in close proximity etc etc, they should behave near equally. You can prove this to yourself by solving the intensity as a simple 1/R^2 problem and very the spacing and the height. Toss in absorption and frensel losses if you want and you'll come to the same conclusion to within a 5-10%.
 
Man Tony, I finished grad school quite a few years ago and now teach freshman/sophmore level classes, I don't do any of that complicated math crap anymore :D

But net conclusion, is while it won't be the same, it won't be THAT much different, plus with the addition of some T5 bulbs (which weren't there before) it really should be a non-issue. Or maybe I should just toss a 250W DE bulb over there, everyone says they suck compared to mogul (or perhaps lumenarc reflectors) but the whole point is to toss some T5 supplimental lighting up there which I can't do with the current size of the reflectors.

Now I just need to track down that starter, or pony up $50 for one I know will work (god I hate being such a cheap ass sometimes).
 
None of that math is necessary. EVERYTHING affecting the intensity of light reaching the bottom of the tank (the reflector, the fresnel effect at the surface, scattering in the water, etc) is linear with respect to the intensity of the lamp. Sure, the distribution will change if there are two lamps, but the amount of light reaching the bottom of the tank will not. The distribution will probably be better, actually, since it will be more even and have fewer shadows.

An interesting side point: perceived brightness is not linear with respect to intensity due to the response curve of our retinas. This means that to our eyes, a 300W light appears only about 40% brighter than does a 150W light!
 
Yeah I know about the perceived brightness, that's one thing I talk about when I talk about how Hipparchus got the magnitude system for the stars... however that is another story :D I don't care how bright it looks to me, I care about how bright it looks to the corals (and perhaps how pretty they look :D)
 
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