Lounge Lighting

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We'd like lighting other than the standard fluorescent tubes for the lounge.

LED Lighting

Everyone seemed to like the idea of LED lighting. James suggested a grid of wires with LEDs at the intersections.

The grid would be made of steel cable attached to eyebolts, with turnbuckles at one end for tension.

Once a grid exists, there are a few different ways to add lights to it.

Single-colour grid, all lights controlled together

Simplest design

This is the easiest to build and drive because the cables don't have to be electrically isolated from each other - two continuous pieces can zig-zag across the room at right angles to each other. The lights can be dimmed, but nothing else can controlled.


Standard Multiplexing

By connecting the rows and columns to microcontroller output pins (through drivers), multiplexing can be used to control each LED individually, like a dot-matrix display. See also here. Since the LEDs aren't on continuously, this could result in dim lights, but that can be mitigated (solved?) by driving the LEDs with more current (eg 1/8 duty cycle at 8 times the rated current).

By using red, green, and blue LEDs, full-colour lighting could be achieved.


The lounge is roughly 17'x17'. 1' appear to be good spacing. Therefore because of fenceposts, a 16x16 grid can be installed. Powers of 2 are a good idea. Easier to deal with than prime numbers. 16x16 = 256 intersections. The grid could consist of single conductors with each intersection having one LED, with a repeating RGB or RGBW (power of 2!) pattern across the grid, or the grid could consist of two-conductor wires (or 1-conductor for ground, 4-conductor for positive - enables the use of common cathode/anode RGB leds) and each intersection could have a board with 4 LEDs (RGBW) - gives 1024 effective intersections.

Brightness and Power Consumption

How much light do we need?

The existing lighting consists of 12 4-foot T8 fluorescent tubes - mean lumens 2800, CCT 5000K, CRI 85. 12 x 2800 = 33600 lm. Assume 10% loss from reflection off an transmission through the fixture - 33600 x 0.9 = 30240 lm. The lights are much brighter than they need to be. We could probably use half that much light: 30240 lm * 0.5 = 15120 lm. (be careful when attempting to compare light output! watch for the angles, and compare units! Lumen, Candela)

SMD LEDs from ledz.com have a 1/2 power angle of 130°. Brightness: Red 110~130 mcd, Green 40~50, Pure Green 250~300 mcd, Blue 70~90 mcd, White 380~550 mcd.

15120 lm / 256 nodes = 59 lm/node.

Using white LEDs alone: 380 mcd = 0.38 lm/sr. 1.38 lm total. 256 white LEDs gives 256 x 1.38 = 353.28 lm. not enough.

OK, try the "High Flux" white LEDs: Not much more expensive. 7.8 lm * 256 = 1996 lm.

Colour Mixing

How does colour mixing work? Eye has different sensitivity to different wavelengths. [1] [2]. [3] - intro to colour theory at some point, or so i hear.

Multiplexing with latching

This reduces the dimness and high peak current problems that conventional array multiplexing can have. Run two parallel grids - one for power, one for control. At each junction, a board holds an LED and a T-type flip flop (JK flip-flop with inputs tied together). Or something. That's the general idea anyways - each node can be latched on with a pulse. Also, a node could have 4 leds (RGBW) and 4 latches.

Multiplexing with shift registers

Run a power grid (+ one way, GND the other). Each node has a 4-bit shift register controlling the 4 LEDs. Shift in from the end. Maybe.

Smart (multi-colour?) LED Modules

The grid could be connected only to power and ground, and each LED module could be intelligent. Communication would occur on the power line. This is the easiest way to use multi-colour LEDs/modules, but it's also the most expensive and requires the most assembly.

I have a smart LED module - it needs a three wire connection... high brightness ones are about $20/ea unless we start fabricating. ~Myrcurial

Reactive Lighting

Add some down-facing motion sensors, and the lights could react to people walking around underneath like EMSL's interactive LED panels.

A new approach - Luxeon-a-likes

None of the other solutions seem feasible. Using lots of LEDs seriously complicates driving - requiring more channels, increasing current/channel, making peak currents very high.
Luxeon-a-like efficiency is twice that of regular LEDs.
Yes, they do require heatsinking. I'm sure we can scrounge up a bunch of heat sinks.

8x8 grid, 1 LED at each node (64 nodes, 64 LEDs)

Repeating RGB or RGBW pattern. 1W/350 mA each. Use linear drivers.
Use the stars from ledz.com - price is about $2 each, so cost for LEDs is ~$128
How much light?
Red: 30-50 lm. Green: 50-70 lm. Blue: 10-20 lm. White: 60-75 lm.
With 21 each of red, green, and blue at full brightness: (21 x 40 lm) + (21 x 60 lm) + (21 x 15 lm) = 2415 lm.
With 16 each of red, green, blue, and white at full brightness: (16 x 40 lm) + (16 x 60 lm) + (16 x 15 lm) + (16 x 67.5 lm) = 2920 lm.
Power consumption?

8x8 grid, RGBW at each node (64 nodes, 256 LEDs)

Could also just lay it out as a 16x16 grid.
Use the stars from ledz.com - price is about $2 each, so cost for LEDs is ~$512
How much light?
(64 x 40 lm) + (64 x 60 lm) + (64 x 15 lm) + (64 x 67.5 lm) = 11680 lm.
Power consumption?
But then there's a problem. Max pulse current for these is only 500 mA - less than twice the constant current. Kinda makes it difficult to trade off duty cycle for current. Maybe the latch thing is a good idea. Or maybe it should be implemented using smart nodes (with linear regulators to keep the cost down).