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If the led's are in series it means that the same current pass all of them and will lit with the same brightness. You will need a voltage supply bigger then 25 * LED Forward Voltage, that's around 50 volts
i'd like to add:
If your supply isnt high (>50) you can use parallel/series network to use that with lower voltage.
For example if you want to use 12V battery to turnon LEDs, you can parallel 5 legs of 5 LEDs (in series + current limiter resistor).
for current control you can use 330 ohm resistor for above example.
He said 'bright leds' those are usually white ones, which means the voltage is going to be closer to 3-4 volts per LED. So it may be as high as 75-100 volts. Equal brightness is not possible doing large series strings like this, the brightness will depend on the variation in manufactoring of the LED's.