Laylat al-Qadr may be seen with the eye, for the one whom Allah helps to see it. That is by seeing its signs. The Sahabah (may Allah be pleased with them) used to recognize it by its signs. But not seeing them does not mean that one will not gain its reward, if one spends that night in prayer out of faith and the hope of reward. The Muslim should strive to seek it in the last ten nights of Ramadan, as enjoined by the Prophet (peace and blessings of Allah be upon him), hoping to earn reward.