[Zensation]

All of the ones I have found online that are specifically for photochemical purposes as advertised by their company are in the ranges of $3000-$12,000. Though, these were all specially suited for photochemistry.

The Metal Halide and Mercury vapor lights that I have been able to find seem to have built in filters to filter out the UV light, which is no good. I don't intend to submerse the light in the solution but just shine it on top of an open stirring beaker.

I found a site in the UK that sells 200-400w lamps that can be mounted or held, with prices around $800 Euros, which isn't that bad, but the advertised spectrum is 350nm up, and I've read the most suited spectrum for photochemical reactions is around 250-260nm. What sort of light can I look for that will provide this? I don't need anything specialized with cooled submersible tubes and all that, and I can probably find a ballast.

[Archer]

It's not just the light, you really need quartz apparatus to house the light in for best results.

It really depends on your application, I have got very pleasing results from putting my reaction vessel on the window ledge in direct sunlight for a few days.

[Zensation]

A few days is a long time! What sort of reaction were you running? Was it stirred?

The SRN1 reactions I am interested in with various alkyl-aryl halides have been reported to be completed in 15-30 minutes in sunlight. Is there a reason it would not suffice to shine the correct frequency light (250nm+) directly onto the [open] solution from above?

These lights can burn the skin if they shine on them for too long. Why would it not be effective in exciting halide molecules if the light is ~ 1 foot away from the stirring liquid? I would venture to claim it is impossible for the air within that 1 foot to absorb all of the UV, right?

Unless Is there something I am missing?

[Archer]

Air is not the problem, the intensity of radiation is proportional to the inverse square of the distance between the source and substrate.

Intensity is proportional to 1/distance². Ideally you need as intimate contact as possible.

My reaction was an oxidation with cumene hydroperoxde in a biphasic mixture.

[Zensation]

http://en.wikipedia.org/wiki/Radical-nucleophilic_aromatic_substitution

I did some further reading, apparently this reaction works without constant irradiation. It seems all that is needed is a radical initiator, due to the chain propagation effect of this reaction. That's nifty.

If this is true, I could just take it outside for a few minutes and then keep stirring it back inside while it goes to completion.

[Archer]

What initiator are you planning to use?

[Zensation]

. SRN1 reactions are generally initiated either by UV irradiation of the reaction mixture in ammonia solution, or by a transition-metal catalyst such as FeCl2

The initiator would be the light.

Though taking a look at the reaction conditions the propagation may come to an end after it starts seeing as the chlorine radical will eventually react to form HCl (later neutralized by the base), and to react with the proton that was abstracted from the initial substrate, it must take the electron from the anion that is causing the  propagation, I do believe.

With the right aryl halide this reaction may not even need light to go, but light would definitely speed it up.

[opsomath]

I have a lamp used for making acrylamide gels which I plan on doing photochemistry with. Salvaged it from a bio lab's throwaways. Anyone ever try this?

[Enthalpy]

Low-pressure mercury lamps are designed to emit at 254nm. Sold as germicidal lamps (Light Sources Inc, Senlights, Hanovia and many more), they should be affordable. Others specialize in photochemical reactors, with already quartz windows.

Medium-pressure mercury lamps emit very little at 254nm, and most at lower energy, in a broad spectrum.

Fluorescent lamps do have filters to attenuate mercury's unconverted UV - glass and the phosphors do already a good job.

Wavelengths below 254nm use excimers lamps. Not the same price as mercury.
http://old.iupac.org/goldbook/ET07372.pdf