Pin 8 Output Voltage varies depending on software?

Other Hardware General Electronics
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I have a windows phone (I know, right?). I've loaded Windows 10 on it and this allowed me to load a couple of programs to the phone. One allows you to control the outputs on the Arduino (Uno R3 in my case) via Bluetooth, the other allows the Arduino to use the phone as a virtual shield via Bluetooth. There are a couple of example projects online. The one for the shield program allows you to turn an LED on with a voice command. The remote project lets you turn on the outputs and thus an LED. I did both projects and noticed that the LED on the shield program is dimmer than when using the remote program. This with absolutely NO changes in hardware or wiring/setup. I've gone back and forth several times with the same results to eliminate a loose connection possibility. I am using pin 8 (digital). I removed the wire that was connected to the anode of the diode and measured the voltage there. The shield program (dimmer LED) was about 4.76 volts and the remote program was 4.87 volts using the same ground. These measurements were with the Arduino powered by the USB, but I've also observed the LED brightness discrepancy with the board powered using a 9V battery. My question is, of course, what causes this? I didn't think a digital output voltage could be varied programmatically. I've posted the two Arduino programs. The shield project required an "ArduinoJson" download from GitHub. This is really just a general function question. My LED doesn't need to be brighter, I just can't understand the behavior. Thanks.

OutputOn-OffWithBluetooth115200Baud.ino (23.6 KB)

VoiceCommandOutput8OnOff.ino (2.62 KB)

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Without looking at your code, I would guess the LED is pulsed which would reduce the brightness.

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hey guys , a little different question from topic
what kind of bluetooth module can be used for this purpose?
I mean there cheap ones & costly ones too, the ones mentioned in example are of sparkfun which are quite costly,
can u give some suggestions or info ?

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"These measurements were with the Arduino powered by the USB, but I've also observed the LED brightness discrepancy with the board powered using a 9V battery. "
5V from USB can be 4.75V to 5.25V, with some loss of voltage across the PTC resettable fuse.

Using 9V battery results in 5V from an on board 5V regulator, and will be 5V.

Bluetooth modules I believe talk to Arduino via serial interface in most cases. I'd buy from a known distributor where you'll be able to get support - Adafruit, Sparkfun, Digikey, Mouser, vs a random source on Amazon, or worse, ebay.