@lifetime17, nice laser, these are "true" pen style hosts, If only Will would reply more, i would buy all his hosts.
So, I found someone on EBAY who sells those small LEDs and I am currently looking at this 100 lot of white LEDs but the owner said I can pick 50white 25green and 25 blue, any idea if these would work? (Too big?). If you can make a schematic of where to solder and the resister I would buy the led and resister now.
http://pages.ebay.com/link/?nav=item.view&alt=web&id=171524832810&globalID=EBAY-US
Thanks,
Those eBay LEDs are 5mm. Probably (way) too big for that host. On the resistor value, it will depend on the LED color (which determines the turn-on voltage = Vf = forward voltage), the max current the LED can handle (sometimes called If = forward current), and the voltage you're feeding it. The voltage to turn on Red LEDs is on the lower side of LEDs in general at 1.65V, Blue and White LEDs, however, need around 2.5-3V. Many (most?) LEDs run at 20mA (= .020 amps) maximum. Some can go much higher, best to check the spec before you try.
Also, the LED brightness varies a lot from vendor to vendor. Typical brightness parameter is MCD. The higher the value, the brighter the LED. MCD = 5,000+ are very bright. Some advertise Ultra Bright, Super Bright, etc. If you want bright, look for that in the description.
If you drive the Red LED with 3.7V with no resistor, it'll probably burn out immediately or soon. The resistor value is calculated as:
Resistor Value in ohms = (Source Voltage - LED_Forward_Voltage) / (LED_Forward_Current in amps)
So driving a Red LED with max current of 20mA from a 3.7V battery we have:
R = (3.7-1.65)/.020 = 102.5 ohms.
Resistors don't come in every possible value so rounding to 100 ohms or 120 ohms will be fine.
As the battery gets weaker, so will the LED brightness which, if fairly noticeable, can be used as a battery charge detector.
I can give you more details if you have any other questions, feel free to PM me.
OVNI