LED Encapsulation for Outdoor Light Element - Page 1
Forum section: electronics / projects

author: 69morpho
author_rank: Newbie
timestamp: April 20, 2015, 06:48:42 pm
content: Hello-I have a project in which I am seeking some technical advice. I will be building 400-500 light elements. The elements will be used outside exposed to sun, wind, snow and rain. The light elements are a 2 inch diameter sphere that will be suspended from a cable. I plan on using high brightness LEDs that would illuminate the balls. The LEDs are mounted on a small star metal clad PCB for heat dissipation (MCPCB). I think it is best that the LEDs and all connections be encapsulated or potted in some kind of UV, weather resistant and non-electrically conductive crystal clear resin or rubber within the ball. The bottom hemisphere of the ball will need to be water transparent to a slightly translucent red or blue. The top half would be clear and does not need to be illuminated.Some of our ideas include:1) Making a 2 part mold and pouring the first half with color, then putting the LED in and the pouring the top half with clear. Wires and suspension hook coming out of the top.2) Buying some of those 2 piece acrylic balls. (Kind of like plastic easter eggs or toy machine balls only perfectly round.) Perhaps we can find them with transparent color and could interchange them with the clear. We could then use this as a mold and clear encapsulate LED within.My concerns are:1) Heat dissipation from the LED itself. We would attempt to engineer a heat sink that protrudes outside the ball.2) Durability of potting material. Material must be UV and weather resistant, it must have to be able to handle heat from LED, must not yellow over time and be crystal clear or perhaps the colored part have some slight translucency to grab some light.Any advise?

author: georges80
author_rank: Frequent Contributor
timestamp: April 20, 2015, 07:21:20 pm
content: Contact companies like 3M, Loctite etc for their recommendations. Go direct to the experts...If you plan to drive the LEDs (you didn't specify type of LED, drive current, Vf etc) continuously, the Star Board they are mounted on will typically NOT provide sufficient thermal heat dissipation (assuming even a 1W LED) without further heatsinking etc.cheers,george.

author: ABroodryk
author_rank: Newbie
timestamp: April 20, 2015, 07:24:17 pm
content: What is the power consumption of your leds? Are they 1W, 3W, 5W or greater? Assuming your leds are 10% efficient then you will be burning 0.9W, 2.7W and 4.5W respectively. Recalculate for the efficiency of your leds to get an idea of the size of heatsink you will require assuming natural convection.So my questions are:Does it have to be a sphere? Otherwise you might consider making the top half a heatsink/hook combination and a plexiglass cover for the led with some kind of O-ring to keep everything water tight? Or pot the heatsink base and led in a clear potting compound keeping the fins clear of resin.

author: 69morpho
author_rank: Newbie
timestamp: April 20, 2015, 07:58:20 pm
content: Attached is the most likely candidate for brightness in LED we would choose. Yes it has to be a sphere.

author: georges80
author_rank: Frequent Contributor
timestamp: April 20, 2015, 08:09:22 pm
content: Again, not enough information... What drive current do you plan to use? Continuous use or will they be dimmed, run for only a few seconds each etc? Ambient temperatures (maximum in particular).You will need to determine all that information before heatsink requirements can be calculated.cheers,george.

author: Kjelt
author_rank: Super Contributor
timestamp: April 20, 2015, 08:12:51 pm
content: You better have a look at low/medium power leds around 100 to 150mA each, put a lot in series and even a few strings in paralel. you need more ofcourse but they are very cheap and have better heat dissipation, solder them to a normal pcb and place some ntcs on the pcb as well for temp control.