+title: RGB Lamp Features
+linktitle: rgb-mechanical
+parent: rgblamp
+ctime: 2012-03-24
+
+The [[rgblamp]] mechanicals are based on a little rectangular lamp purchased at
+IKEA. The CREE LED module is placed on a 1/2 inch think heat sink designed for
+the module, and that module is mounted inside the lamp in place of the standard
+screw bulb mount.
+
+There are several challenges with this design. First, the LED module must not
+exceed its thermal specs during operation. Second, the lamp must not expose
+human eyes to the direct output of the LED module. Finally, we need to find a
+way to mount both the module and the electronics.
+
+# Thermal issues
+
+The
+[datasheet](http://media.digikey.com/PDF/Data%20Sheets/Wakefield%20Thermal%20PDFs/882_Series.pdf)
+for the 0.5 inch thick [heat
+sink](http://search.digikey.com/us/en/products/882-50AB/345-1104-ND/2640527)
+specifies a 60 degree C rise in temperature when dissipating 9W with natural
+convection. That is 60/9 or 6.67 C/W. Since the [CREE LED
+module](http://search.digikey.com/us/en/products/MCE4CT-A2-RGBCW-STAR-IND/955-1043-ND/2357817)
+will be limited to 350 mA at about 3.2 V by the control circuitry, maximum power
+dissipation is 1.12 W per LED, or 4.48 W for the entire module. In ambient air,
+the 0.5 inch heatsink will see a rise over ambient of about 30 degrees Celcius.
+So if room temperature is 30 C (86 F), the temperature and the juntion beween
+the module and the heatsink should be about 60 C. I failed to locate a maximum
+junction temperature for this module, but 60 C is not too high for most other
+LEDs out there. To ensure good thermal contact, the module was secured to the
+heat sink with machine screws and a bit of thermal paste.
+
+In operation, the lamp when tested in operation suggests the heat sink is
+actually performing a bit better than the data sheet numbers suggest.
+
+# Eye protection
+
+The problem with the IKEA lamp used is that it is open through the top. This is
+an advantage thermally because the lamp acts like a chimney, allowing cool air
+to enter through the opening in the bottom -- which was left open for
+ventilation purposes -- and warmer air to rise out of the top. The downside is that a
+person could easily look into the lamp from above. These high power modules can
+cause retinal damage, so this is a problem. The solution was to mount a few
+inches above the LED module a diffuser. The diffuesr spreads the light nicely
+while also blocking direct visual exposure of the module LEDs.
+
+# Mechanical mounting notes
+
+This was a quick project, so the mechanicals are of the basic prototype variety.
+The electronics are mounted on perfboard in a small project box, and a short
+section of 28 AWG cat 5e cable delivers current to the LED module. A DC wall
+wart is used for power, and the heat sink is mounted in the lamp with hot glue.