How many leds can i connect to arduino powered from usb

Question in topic. Led's are red. (sorry for bad english)

USB can supply 500 mA. Figure 50 mA for the Arduino leaving 450 mA for everything else. LED’s take about 20 mA each so 450/20 = 22.5. So that means you can have as many as about 22 LED’s on at one time. If your LED’s are multiplexed that can extend to hundreds as long as no more than 22 are on at one time.

Keep in mind that while John's calculations are correct, you can't simply hook up that many LEDs onto the Arduino pins. Each pin can only supply 40mA. At 20mA per LED, that's 2 per pin. You can get lower current LEDs and drive more of course, but ultimately you will run into that limit. External drivers is one solution.

Thanks for help. I don't want make from my arduino that: