But recently I had a special case where I wanted a baseline level of heavily diffused light, combined with another component that was a lot more directional.
No problem, just place a small source very close to the diffuser that's wrapped around the subject, so that only a small part of the diffuser would light up super bright.
The usual way to do that is with a fiber optic bundle.
But this time I decided to try something a little different. It worked out OK, so I thought I'd post it out just in case it might be helpful to somebody.
Here's an illustration of the result. What we're seeing here is an index card resting by gravity on the face of two Ikea Jansjö lamps. The lamp on the right is normal; the one on the left has been modified so as allow much closer access to the LED element. In addition a short piece of opaque tubing has been placed around the LED to restrict its output to be the diameter of the LED element. The result is a very small spot that contains a substantial fraction of the entire LED output.
Here are the lamps without the index card. Very briefly, the one on the left has had its lens, reflector, and the front roughly 10 mm of the housing / heat sink removed.
Here's a comparison of the modified head versus a stock head that has only had its lens removed.
The modification process was to
- start with the stock head
- pop out the clear plastic retaining ring that holds the plastic lens in place
- remove the two screws holding the reflector in place
- harvest two plastic washers by cutting them free from the reflector
- temporarily replace the washers and screws
- unsolder the two power wires
- remove the circuit card, whose back side is covered with heat sink paste
- clean up the head
- saw off 10 mm of the aluminum enclosure / heat sink
- apply new heat sink paste
- replace two plastic washers and screws
- resolder power wires
- pre-shrink a piece of 3/16" heat-shrink tubing
- trim tubing to length and place over the LED.
Clearly it would be more light-efficient to use something white instead of that black tubing, but hey, it was handy, it worked OK, and it can be replaced later if that's important.
A couple of things about heat management:
1. The modified head definitely runs warmer than the unmodified one, because it provides less surface area to dump heat into the surrounding air. But it still seems to be a safe temperature. After running all night, the normal head is clearly warm to the touch and the modified one is still short of painfully hot. I'd guess 20 degrees Fahrenheit increase, possibly 30.
2. That part about pre-shrinking the tubing is important. The LED element gets plenty hot enough to shrink the tubing by itself, if you don't. You can trust me on this.