The Cadillac of Pendents (A Custom King original)

[Chiefmcfuz]

Ok I think I got it.

I think what is being said here is that there is the retro kit which is attached to the suspension kit there is a space where the acrylic hood is attached to just the suspension kit. The retro kit is not attached directly to the acrylic so there is room persay in between them and the acrylic is "Safer" than if it were attached directly to the light. Ok now lets talk about material failure, convection, conduction, and my favorite (not really) and everyone else's fire.

Ok at some point in time we know acrylic fails when exposed to prolonged heat, it becomes brittle and cracks Convection is the heat radiating off that light kit up into the acrylic because heat rises, conduction is the heat traveling through the metal hardware and in turn being transferred to the acrylic, Now with all of this adding up you get the acrylic failure. of course the longer the lights are on the quicker this will happen but eventually it will. So when eventually when it does the acrylic will either fal into the tank, onto the light, or on the floor. Now we all know that when talking about reefing Murphy's law applies 95% of the time. So the chances of this thing falling on the floor are slim to none. You run the risk of contaminating your tank with compromised acrylic or having it damage the tank causing a break. You also run the risk of it or part of it falling and getting hung up on the light kit causing it to melt and possibly cause a fire.

Lastly I want to point out that sudden changes in weight distribution on mounting kits like this can cause a collapse and that could result in the fixture falling partially of completely into the tank or on the floor possibly causing a fire.

I hope I helped clarify a few things on both side. I may just be a Volunteer firefighter but I have been doing it 17 years was a firefighter, Lieutenant, Captain, Assistant Chief and Chief of department, my term ended and became an ex-chief for 3 years and now I am an Assistant Chief again. I have seen, fought and helped investigate pet related fires in the past 17 years as well. Hope my qualifications speak for themselves and I am just looking out for everyones safety here.

 

[KathyC]

Interesting post from our very own Fire Chief.

Custom King..I'll start by saying your acrylic work is beautiful and I've admired many of the things you have built, but I find this light is making me nervous.
Do you have pics of previously built ones and perhaps can show us the pics of what they look like after being used for any extended amount of time?
I get many questions about the acrylic covers I make and their reaction to heat from MH's ..and those are usually used a minimum of 6" away from any lighting.

 

[ellebelle]

Actually, upon further reflection, this could work without failing.

Radiation, convection and conduction are the ways that heat is transferred. A reflective surface (like a standard aquarium reflector) will stop the heat from being transferred up. That is essentially how a thermos works, right? Heat is reflected away from a thermos using a reflective surface. It's also why many heat insulators come with a reflective packaging. It's also why the tops of all of our canopies don't get ridiculously hot to the touch even when running 400w bulbs. My reflector is in direct contact with my canopy, and the top doesn't even feel warm. (This is likely because the reflector is dealing with the radiation and wood is poor conductor of heat because of its air content - see below).

Air is actually a very poor conductor of heat. In fact, the best heat insulator would be a total vacuum where there are no molecules at all to transfer the heat from one place to another. But an empty space works pretty well. That is actually the principle that several kinds of foam insulators are based on.

I think my biggest worry would be the way that you've attached the reflector and the bulb to the acrylic. Depending on what kind of metal is used for the retrofit, that COULD be a good conductor of heat and could bring heat from the bulb up to the acrylic canopy.

So, in sum:

1) The acrylic work is very nice on this.
2) I think the physical principles behind the construction of this are good.
3) I'm still not sure I'd personally take the risk, no matter how cool it looks.

 

[fishguy23]

Great debate...!!!:splitspin

 

[Chiefmcfuz]

Very nice Lissa, Heat rises.

 

[Wes]

Very nice Lissa, Heat rises.

and also travels via conduction. The reflector does not block heat, it conducts it. The heat will travel through the reflector, through the mounting hardware, into the acrylic... Which will eventually result in a failure.

If you somehow mounted the reflector to the acrylic with some sort of heat resistant material, it might survive the test of time...

 

[h20 freak]

Ow, my eyes hurt from looking at the picture:Yikes:

 

[jejton]

Actually, upon further reflection, this could work without failing.

Radiation, convection and conduction are the ways that heat is transferred. A reflective surface (like a standard aquarium reflector) will stop the heat from being transferred up. That is essentially how a thermos works, right? Heat is reflected away from a thermos using a reflective surface. It's also why many heat insulators come with a reflective packaging. It's also why the tops of all of our canopies don't get ridiculously hot to the touch even when running 400w bulbs. My reflector is in direct contact with my canopy, and the top doesn't even feel warm. (This is likely because the reflector is dealing with the radiation and wood is poor conductor of heat because of its air content - see below).

Air is actually a very poor conductor of heat. In fact, the best heat insulator would be a total vacuum where there are no molecules at all to transfer the heat from one place to another. But an empty space works pretty well. That is actually the principle that several kinds of foam insulators are based on.

I think my biggest worry would be the way that you've attached the reflector and the bulb to the acrylic. Depending on what kind of metal is used for the retrofit, that COULD be a good conductor of heat and could bring heat from the bulb up to the acrylic canopy.

So, in sum:

1) The acrylic work is very nice on this.
2) I think the physical principles behind the construction of this are good.
3) I'm still not sure I'd personally take the risk, no matter how cool it looks.

Without going into details ( of which my knowledge is limited to a few physics and chemistry courses anyways ) just a simple test will show that a reflective source will get very hot. Touch a nice chrome car part after the car has been sitting in the hot sun for a few hours. It will be pretty hot. Yes it will reflect radiated heat but it will also conduct heat as well. Not saying that's what will be happening here as I am not a material expert or engineer; just trying to show that a reflective material can still get pretty darn hot. Also I believe thermos's work by creating a partial vacuum between layers while foam relies on air but also the properties of the foaming material itself ( such as asbestos ).

 

[ellebelle]

Simply speaking, a thermos generally has two reflective surfaces, one on the outside and one on the inside, with a vacuum in between. The reflective surface on the inside will keep heat in and thus keep hot things hot and the reflective surface on the outside will help keep cool things cool. The vacuum is to stop heat transfer between the two surfaces.

I think that our reflectors are reflective enough to bounce back a good porportion of the heat. Otherwise our hoods would be hot all the time as aluminum is an excellent conductor of heat and (if I am not mistaken) our reflectors are all aluminum based metal alloys. My table gets hotter after my laptop has been sitting on it than my hood does after my MH has been on all day.

 

[Wes]

fwiw, aluminum is an excellent heat conductor. Thats why beer in cans get cold faster

 

[Domboski]

Everyone has made good points here. The physics may be on your side as ellebelle has pointed out but do we know what material was used to connect the reflector to the acrylic? When a firefighter points out a potential problem for fire I think you should take notice.

IMO the potential for fire outweighs the visual benefits of the fixture. I'd hate for my apartment to catch on fire and then wish I didn't take the risk.

I never want to poke holes in new ideas but with the cost of shipping it would greatly benefit fixture manufacturers to use acrylic but they do not. My guess it is because of the risk for fire.

 

[Wes]

Simply speaking, a thermos generally has two reflective surfaces, one on the outside and one on the inside, with a vacuum in between. The reflective surface on the inside will keep heat in and thus keep hot things hot and the reflective surface on the outside will help keep cool things cool. The vacuum is to stop heat transfer between the two surfaces.

I think that our reflectors are reflective enough to bounce back a good porportion of the heat. Otherwise our hoods would be hot all the time as aluminum is an excellent conductor of heat and (if I am not mistaken) our reflectors are all aluminum based metal alloys. My table gets hotter after my laptop has been sitting on it than my hood does after my MH has been on all day.

conductive heat is the concern here. A thermos works because the vacuum is an insulator that helps prevent conduction.

A Thermos with reflective surfaces and no vacuum will lose heat faster than a thermos with vacuum and no reflective surface.

Concerning the table getting hotter from the laptop:

You are comparing the contact surface on your table to the surface opposite of contact from your MH lighting. Wood is a good insulator. Compare the underside of your table to the top of your canopy

 

[Domboski]

fwiw, aluminum is an excellent heat conductor. Thats why beer in cans get cold faster

This is true. When I was working in the structural design field one of the hot topics was beer in a plastic bottle. Often people think beer in glass or aluminum bottles are colder because they feel cold to the touch. Well many engineers told me that was the coolness escaping the liquid and that plastic was a better insulator to keep the beer cold.

I interpret this to mean it may be better to have a conductor like aluminum to pass the excess heat created by the bulbs / ballasts as quickly as possible. I'm not sure what the effect heat will have on acrylic / plastic since it is an insulator. My guess it will eventually break down in a number of ways.

Hopefully someone with an engineer background will chime in. Sanjay where are you? :splitspin

 

[Domboski]

I cannot tell from the pictures, if there is any active cooling put into place. If not, just relying on air to provide the insulation between the metal and the acrylic is not a good idea in the long term. Acrylic over the long term will not handle the heat, resulting in heat distortions, and in the worst case melting of the acrylic. I have a melted MH retrofit JBJ nano hood sitting in my basement, if anyone wants to see it.

Another question I have is how much heat is needed to burst wood into flames versus the amount of heat needed to melt acrylic? Many wood canopy setups have the reflectors fastened to the wood. I'm guessing much less heat is needed to melt plastic.

 

[Chiefmcfuz]

Different types of wood have different flashpoints. Plastics will burn too at different temps as per the type of plastic.

 

[kimoyo]

conductive heat is the concern here. A thermos works because the vacuum is an insulator that helps prevent conduction.

A Thermos with reflective surfaces and no vacuum will lose heat faster than a thermos with vacuum and no reflective surface.

Hey Ellebelle,

I have to agree with Wes on this one. I think your getting confused on the term reflective surface and how it applies to light vs heat (light reflection vs heat barrier)

An example of this would be when an acrylic top cracks at the corner due to metal halides. Most people don't realize that its not the light from halide, but heat and the tight corners in the opening (which stresses the tank). The heat takes an already stressed corner and stresses it even more until it cracks.

Because metal is a conductor there is something called the 'skin depth. Not all the light is reflected which is why it heats up. Some of it enters the conductor and takes a certain distance to be reduced and its calculable. It has to do with something called the free current density not being zero in a conductor unlike in a vacuum or in glass (which is an insulator) where it is zero. With glass some light goes through and some light gets reflected back at you. With metal some light gets reflected back at you but some of it (against common preception) goes into the metal and dissipates.

The point being that the radiation isn't the concern but the conduction and convection are. It would probably be less on an issue with t5's or power compacts but I've never tried it.

 

[cali_reef]

Heat travels in all directions away from the source and typical MH reflectors used are not efficient in deflecting all the heat. Aluminum reflectors will reflect some heat away, but have you try touching the reflector's top surface after the light has been on for a few hours? that heat is slow cooking the acrylic above it and heat will break down acrylic over time.. Someone should ask Sanjay on efficiency of reflectors, heat transfer, and the acrylic's failure probability, he should be full of that knowledge.


PS. The Elos line of MH pendants are made from ABS plastic, ABS fairs better with heat and those do get pretty damm HOT too.

 

[cali_reef]

fwiw, aluminum is an excellent heat conductor. Thats why beer in cans get cold faster

They also get warm quicker, stick to glass bottles :lol2:.

 

[kimoyo]

I just did a search on skin depth and I can't believe wikipedia actually has a page on it. http://en.wikipedia.org/wiki/Skin_depth
A few years back when I was in school you could only find this stuff in textbooks.

 

[Domboski]

Paul you're giving me a headache :splitspin J/k Good info. What does it mean though? Do you think the acrylic will have a problem?