[thedoc (OP)]

Dan Higgins asked the Naked Scientists:
   I recently bought a Star Shower laser light - it projects small bits of green and red light onto surfaces to look like Christmas lights.  I bought it to project onto an 80' pine tree in my back yard, and it actually looks fantastic. Just like Rockefeller Center! However, I am concerned that the light may damage the tree.  Am I correct to worry about this?
What do you think?

[alancalverd]

It's unlikely to do any more harm than ordinary christmas lights. Fortunately trees don't have eyes, so you won't do any retinal damage!

[Don_1]

So far as I am aware, low power lasers would not have any effect on a tree of this size.

I believe that some experimentation with lasers on germinating seeds have shown different lasers have different effects on them. None seem to be detrimental.

I think of greater concern, assuming this unit does emit laser light, would be where and at what level the lamp is placed and whether any laser light misses the tree. Stray beams entering windows could result in problems. Even low power laser light shone directly onto the retina can be dangerous. And please do consider not only humans, but wild animals too. Any arboreal animal and birds could be at risk and they are heavily dependant on their vision.

[evan_au]

I assume that this would be an "eye-safe" laser. Look for a marking like "Class 1 laser" on the casing. These are actually quite safe, even at short range.

From the description, I assume that it has some optical device to spread the red & green laser beams out into multiple beams in different directions, each with a much lower power.

Try not to point it too much into the sky, as pilots could have their night vision impaired. But with many beams of very low power, I don't imagine it would be a problem.

[chris]

Fortunately trees don't have eyes...

...but potatoes do - are they at risk?

[evan_au]

Fortunately trees don't have eyes

They do have chloroplasts, which are light-sensitive.

Chloroplasts are optimized to work in sunlight at intensities around 700W/m², not at decoration intensities of perhaps 1-10mW/100m². So an eye-safe laser won't damage your tree.

However, I once saw smoke rising in a public area, and I realized that a young man was shining a green laser on a piece of paper in his hands. This caused charring of the paper, and could have been enough to set it alight; it would certainly have been enough to burn holes in a leaf. However, I am sure it was more powerful than Class 1, and it was focused to a point, rather than being spread over a large area like the Christmas decorations described here.