light reflection makes light darker?

[deleted-900497]

Hello everyone,

I am a teacher in Belgium, so forgive me my bad English.
Lately I got a strange question of one of my students while he was working on a project about lights in glasshouses.

the light he used was a standard fluorescent tube, put in a mirror-like box to reflect. by accident he noticed that a mirror on the floor reflected the light back up (what is normal). So he tought that if he reflect the light back in the mirror-like box, the amount of light (lumen) would double. Although, when he did this, he noticed that the light got darker instead of brighter.

I also tested this, and indeed this is the case.

Is there any explanation for the phenomena?

thanks for your answers

Alex

Moderator note: Hi Alex, I'm cross-posting your post to the Grades 9-12 Physical Sciences forum, so the experts there can also help you. Thank you!

[norman40]

Hi Alex,

I'm not sure that I understand your experimental set up. But based on your post it seems that you are measuring intensity of reflected light. And the measurement is made near the original light source.
If this is the case the reflected light intensity would be lower than that of the source due to the greater distance that the reflected light travels.

I hope this helps. Please post again if you have more questions.

A. Norman

[deleted-900497]

Ah thanks Norman. But it’s not quite like this.

Let me explain the situation:

In a greenhouse you have lights. The light shines down on the plants.
The idea of my student was to put a mirror on walkway between plants (since the light falling there is lost). The mirror reglects the lightbeam back up into the light armature. And so again bounce back down.

But when he used the mirror, it seemed the light intensity on the floor suddenly got darker.

Thank you