It's not ENOUGH light eh? I mean look at the plant. Barring buying a PAR meter get these guys to talk you through using a phone app for determining light intensity. They're not going to give you a light with these pictures.
Yep. If you're an iPhone user, download the Photone App and use it. But use it in tandem with the calculator on their website.
https://growlightmeter.com/calculator/
There is Photone for other phones, but they're not as accurate as with the Apple. I'm sure some Samsung users may have other advice for their platform.
The app is free and you can buy the profile for QB style lights for $5.99. It will give. you the PPFD, Lux & even calculate the DLI. I generally use the app for PPFD then plug it into the calculator on the website, which allows you to play around with the actual week of your grow, how much light/dark and what the PPFD is. From there you can tweak an adjust any of those parameters to a pretty idealized setting.