Light shield breaking

[charlie]

well, i'm tired of fixing this piece and am looking for suggestions that i may not have thought of.

i have a wall niche with a (par30?) incadesant lightbulb in the floor. i made a 2 layer 16" round disk. i cut a 4" circle out of the middle, added 2 4" pieces of clear, and fused and annealed correctly, i thought.

in use, it sits on 1/4" spacers i fused up to allow the heat to escape outwards.

i used to keep a blown glass vessel on top of the hole. the light then shines up through the clear to illuminate the vessel from within, and looks great. it has a very narrow foot (about 2" in diameter oval shaped). everything worked ok for a long time.

my wife decided the cat was getting too nosy, so replaced the vessel with a clear glass vase, which has a 6" flat base. after the light is lit for about 10 minutes, the platter self destructs. the last time it was in about 6 different pie shaped pieces. i fused it back together, and last night it again snapped, this time exactly in half.

my guess is that the larger foot on the vase is acting as a better heat sink, causing a difference in heat across the piece, thus causing thermal fracturing. the smaller foot on the vessel allowed greater cooling from the top surface of the platter radiating better than the thick solid glass foot of the vase.

the alternatives i've come up with are:

replace the incadesant light with a florescent (not a very good idea since there's a dimmer on the circuit, which can't be used with florescents). halogen aren't any better than incadesants in terms of heat output.

increase the height of the posts (how much?)

increase the height of the posts, add another sheet of glass over the light on smaller posts (to prevent the heat from reaching the top platter?). i'm not sure that will work, since the inner shield will heat up, then radiate to the top shield.

glue the vessel down to the platter (not something that's really acceptable).

thanks.

[Linda Landauer]

I use neon.

Linda

[Kevin Midgley]

Try light emitting diodes. No energy cost and last 100,000 hours. Look for a regular screw in one used for fire exit lights. The screw in bases come in small and regular bulb size. You should be able to find them at a lighting/electrical wholesaler.Kevin

[charlie holden]

(snip)

my guess is that the larger foot on the vase is acting as a better heat sink, causing a difference in heat across the piece, thus causing thermal fracturing. the smaller foot on the vessel allowed greater cooling from the top surface of the platter radiating better than the thick solid glass foot of the vase.

the alternatives i've come up with are:

replace the incadesant light with a florescent (not a very good idea since there's a dimmer on the circuit, which can't be used with florescents). halogen aren't any better than incadesants in terms of heat output.

increase the height of the posts (how much?)

increase the height of the posts, add another sheet of glass over the light on smaller posts (to prevent the heat from reaching the top platter?). i'm not sure that will work, since the inner shield will heat up, then radiate to the top shield.

glue the vessel down to the platter (not something that's really acceptable).

thanks.

Or you could put the vase up on little acrylic feet so it sits off the glass a little.

The way you describe what you think is going on seems a little mixed up. I think you're right that the vase is acting as a heat sink and that the smaller vessel allowed more cooling. The key is even cooling versus uneven cooling. It's not that the vase is preventing the glass from cooling. What it's doing is cooling it too much. It is soaking up much more heat into its massive base than is being radiated to the air around it. The problem is that the cool spot is concentrated while the glass around it gets too hot.

Thus, if you lift the vase up a little off the glass it will heat and cool more evenly.

[Brian and Jenny Blanthorn]

well, i'm tired of fixing this piece and am looking for suggestions that i may not have thought of.

i have a wall niche with a (par30?) incadesant lightbulb in the floor. i made a 2 layer 16" round disk. i cut a 4" circle out of the middle, added 2 4" pieces of clear, and fused and annealed correctly, i thought.

in use, it sits on 1/4" spacers i fused up to allow the heat to escape outwards.

i used to keep a blown glass vessel on top of the hole. the light then shines up through the clear to illuminate the vessel from within, and looks great. it has a very narrow foot (about 2" in diameter oval shaped). everything worked ok for a long time.

my wife decided the cat was getting too nosy, so replaced the vessel with a clear glass vase, which has a 6" flat base. after the light is lit for about 10 minutes, the platter self destructs. the last time it was in about 6 different pie shaped pieces. i fused it back together, and last night it again snapped, this time exactly in half.

my guess is that the larger foot on the vase is acting as a better heat sink, causing a difference in heat across the piece, thus causing thermal fracturing. the smaller foot on the vessel allowed greater cooling from the top surface of the platter radiating better than the thick solid glass foot of the vase.

the alternatives i've come up with are:

replace the incadesant light with a florescent (not a very good idea since there's a dimmer on the circuit, which can't be used with florescents). halogen aren't any better than incadesants in terms of heat output.

increase the height of the posts (how much?)

increase the height of the posts, add another sheet of glass over the light on smaller posts (to prevent the heat from reaching the top platter?). i'm not sure that will work, since the inner shield will heat up, then radiate to the top shield.

glue the vessel down to the platter (not something that's really acceptable).

thanks.

What does the glass bowl sit on ??

What about sitting it on a double glass shelf of say 1/4 glass spaced out slightly

And sandblasting the under side of the shelves slightly

This should help in ur evenivity

[charlie]

I use neon.

Linda

can you get neon in regular bulb bases? a par30 is a very short lightbulb in the first place, and i don't really want to rewire the socket. also, i don't believe neon is dimmable either.

[charlie]

Try light emitting diodes. No energy cost and last 100,000 hours. Look for a regular screw in one used for fire exit lights. The screw in bases come in small and regular bulb size. You should be able to find them at a lighting/electrical wholesaler.Kevin

that's a good idea, but is it short enough, and is it dimmable? i assume the dc voltage converter is in the base like power compact bulbs?

[charlie]

Or you could put the vase up on little acrylic feet so it sits off the glass a little.

The way you describe what you think is going on seems a little mixed up. I think you're right that the vase is acting as a heat sink and that the smaller vessel allowed more cooling. The key is even cooling versus uneven cooling. It's not that the vase is preventing the glass from cooling. What it's doing is cooling it too much. It is soaking up much more heat into its massive base than is being radiated to the air around it. The problem is that the cool spot is concentrated while the glass around it gets too hot.

Thus, if you lift the vase up a little off the glass it will heat and cool more evenly.

i hadn't thought of too much cooling, but that sounds reasonable. the base of the vase is 6" across, but it's also about 1.5" thick, so is really massive.

that's a great idea. i'm re-re-re-refusing it now, but i'll give this a try.

[charlie]

What does the glass bowl sit on ??

What about sitting it on a double glass shelf of say 1/4 glass spaced out slightly

And sandblasting the under side of the shelves slightly

This should help in ur evenivity

the glass vase sits directly on the platter, absorbing the heat directly. since they're both so flat on the bottom, they have a large contact area, which is probably conducting heat very well.

i'm going to try elevating the vase first using some bumpons. my next thing to try is the double shelf.

why would sandblasting help in distributing heat differently?

[Linda Landauer]

Others, on the board, have made better suggestions for your application. You would have to re-work your lighting arrangment, and probably change the wall switch (the easy part) After trial and error, I have found that neon works well for me. Less heat, practically lasts forever.

Linda

[Kevin Midgley]

The LED lights come in various outputs etc. I do not know if they are dimmable. They are cold running and just screw in the socket. The ones I have seen for the fire escape lighting units are the size of a standard light bulb with an array of led lights mounted on the core of the "bulb" in a U shape around a popsicle stick type core. It is the simplest solution I know of to your problem. Apartment buildings are using them and saving the cost of the bulb in less than a year's worth of usage. Kevin