Can’t I just buy one bulb and put it a few feet away?
I get this question a lot, surprisingly. People don’t want to buy a $5000 to $10,000 curing rig, but also don’t want to spend $100. You have to be realistic when you are designing a curing rig, and be willing to spent at least a little money or you won’t get the results you want. Most curing rigs needs 4 to 16 lights, meaning a cost of $280 to $1000, but this includes the lamps, ballasts and lamp holders. it can be done a little cheaper if you use off the shelf fixtures, which will be slower, but still work. Where you don’t want to skimp is the number of lamps you use, because that affects more than time, it affects quality of cure.
You can buy twelve Solacure Curall curing lamps for $360, power it with $180 worth of F32 fixtures from Home Depot, and have one hell of a rig. It won’t be super fast, but it will be fast enough, and for under $600 have a rig that will cover guitar bodies, or necks, or violins. Or for $200 you have a rig for curing pool cues or fishing lures. For another $100-$200, you can have one that does it industrial speed and has twice the life of the regular lamps. You don’t have spend thousands, but you have to be willing to spend a few hundred if you want a serious curing rig fit for at least part time use.
When you cure an item, you need enough lamps that it effectively covers the entire item. Let me give you an example using the easiest thing in the world to cure, a 2ft x 2ft flat piece of material. If you use one bulb, you would have to be about 2 feet from the item in order to have any semblance of even coverage, meaning the ends are about as far away as the middle. Using the Pythagorean Theorem, that puts us at about 2.25 feet away from the edges and 2 foot from the center, a difference of about 12%, which is acceptable. Any lower, and the reflector will prevent the edges from getting much of any light, so the middle cures, but it fades out to the ends, which won’t cure at all.
Let’s compare this with an optimum distance of 3 inches away. Using the Inverse Square Law, this means that the amount of light hitting any cubic inch of board at 2 feet vs 3 inches, gets 1/64th as much power. Yes, it takes 64x longer to cure. A 3 to 5 minute cure is now 192 to 320 minutes. Three to five hours. Going cheap and using 4 lamps would let us do this cure in about 10-15 minutes (see notes below), using 8 lamps and we are back to our 3 to 5 minute range. It is fine to go cheap, but if you go too cheap, you shoot yourself in the foot.
Generally speaking, you can keep your project as close to the lamps as the lamps are apart. Lamps that are 6 inches apart can support having the project 6 inches from the lamps. Going over 6 inches means you quickly and radically decrease the effective power, and enter the realm of wasting your time.
It is better to use more lamps in cheap fixtures than it is to have just a couple of lamps in high output fixtures. The total number of lamps is more important than the wattage you put to each lamp. It might not be intuitive or obvious at first sight, but trust me, this has been tested over and over again. Most of my testing is done with 6 to 8 lamps run in lower power mode, simply to show what you can do at the lowest power level, and I’ve tested UV lamps for curing more than anyone I know. The more sources of UV, the better, every time. The smaller the distance to the UV source, the better, every time.
So if you have to skimp, skimp on the power and don’t skimp on the number of lamps. This will guarantee you have the best coverage, even coverage that will let your project cure evenly, without any wierd artifacts. It will also let you put the lamps closer and guarantee a cure time that is much easier to live with.
Notes: 4 lamps at 7 inches apart covers the area, 7 inches from the material is just over twice, so the power is reduced by 80%, but you have overlamp from other lamps (compounding the Inverse Square Law) so you end up closer to 50% to 60% of the original power per square inch, thus 10-15 minutes). The Inverse Square Law is based on a single point of light, and the mathemetics get exponentially complicated as you add sources of light, to the point of no longer being applicable, if you add enough lights. If you are turning the item in front of a flat panel of lamps, the math also gets tricky, but distance is still your enemy.