This “No light on display” is usually an internal issue with the LCD connector. However, Apple recommends some processes to practice on your phone to make sure the black screen is not a software glitch.

• Force Restart your iPhone
• Connect the lightning cable, charge it for 10 minutes. Then try force restarting the iPhone
• UNCONVENTIONAL: But press the screen into the phone so it may reconnect any dislodged LCD connector. This fix is not recommended however it resolved a lot of the user's Black Display issue