In the process of retrofitting lighting into new and existing designs, I come across particularly problematic situations that no products on the market seem to exist. The most recent was a single head pedant I needed a light source with a light pattern somewhere between an old R20 spot and a PAR20 Flood, at around the R20 flood light output. The fixture was designed around the R20 and its soft beam.
I tried a couple commercial R20 LED products, and found them all to be too harsh and splashy, and too narrow in distribution. So, I figured, how hard can this be? I was impatient and tired of buying stuff that don’t work…
Igor! gather me up some parts!
With a heat sink from an older project salvaged from a spare parts bin, a PAR20 cadaver, a tortured to its death screw-base CFL lamp, a fresh 4W 120VAC Acriche LED and my precious collection of epoxies (glue is what holds the world together) – I headed to the lab. The surgery started with cutting the PAR lamp apart with a glass-cutting band saw to separate its optic head from the body. Next was to cut the socket off the plastic CFL ballast compartment, leaving its remains on the floor. After soldered the leads onto the LED, it was glued it to the heat sink with thermal epoxy, then joined to the PAR 20 optic with standard 5 minute epoxy. Wires lead through the heat sink into the socket, grafted to the internal lead wires left from the CFL separation. I filled the socket with epoxy putty to stabilize it and keep the nervous system in its place, then pressed it onto the back of the heat sink. It was done… and not a drop of blood was spilled.
LEDs bring a lot of creative potential to the lighting market. At this creative front will be artists who apply them in unique ways outside the mainstream general illumination marketplace. I’m one of them in fact. Gone are my days of fooling with halogen lamps and transformers – now its LEDs, drivers and power supplies… and heat sinks.
The first wall hit in application of LEDs is their output and thermal dynamic. In halogen lighting, the fixtures got hot, no big deal. As long as it wasn’t peeling flesh or raising a blister, its was fine. LEDs don’t work that way. Long before the lighting portion gets hot enough to raise a blister, the LED is fried, game over.
Ultimately, the goal of an artist in creating a new work of light is to generate as much light as possible in the smallest, most innocuous package. That makes LEDs at once attractive, and a problem. To illustrate, a 350mA 1W LED requires very little thermal management to survive. Glue or screw it to plate of aluminum or copper and its happy. Problem is, the amount of light is pretty weak, between 35 and 60 lumens if you want 3,000k color with good color rendering (yes, artists do care about color – a lot.) That’s a long way from the 600 to 800 lumens we were used to in halogen sources. Optimally, for a task light with a good optic (wide smooth beam), gettting to around 350 to 500 lumens is optimal. This means more energy. At 700mA, 100 lumens is attainable, and lands us in the 3 to 4 watt range. Three is always better than 10, so this sounds like the way to go. Problem is, a 3W LED is exponentially more demanding thermally than that 1W device. These higher energy devices demand heat sinks, real life thermal management, with airflow and everything.
This is my very first functional LED task light, completed at the end of 2005. Construction is welded steel. Originally, the main components of this fixture (2004) were designed for a 12V/20W Halogen bi-pin lamp that created an overheating of the lighting head and poor light output. This was changed to (12) 1/2W Nichia HB LEDs (2800k) mounted to PC board with through hole thermal connection to the heat sink, as an experiment and proof of concept for the application of LEDs to provide greater light output for the same or less energy. Light on the task surface was either 70FC or 150FC, with a very wide distribution, as there is no secondary optical control. An aluminum heat sink inside the lighting head maintains reasonable operating conditions for the LEDs (under 60C TJ), while remaining cool to the touch. The horizontal arm ratchets up and down, the red arches are fiberglass springs that tension the ratchet. The parallel link on the head and arm keep the head level when it is adjusted up and down.
Some wonder why I am such an enthusiast for lighting in general. That’s easy – Lighting is COOL! As an artist at heart, lighting is appealing, as it shapes the visual experience of observers as much as an oil painting hung over a couch. Lighting is both ethereal (it exists, yet is untouchable), and mechanical (requires hardware to manipulate and generate illumination). There is nothing else in the universe of human endeavor that blends art and science in this way. If this were all just about illumination of space to enable and excite human vision, there is enough meat here for anyone to enjoy a lifelong pursuit of it. But, this no longer the case. Continue reading “Opportunities in the Lighting Universe for True Masters”