On Sat, 13 Aug 2016 10:29:28 +0100, Davidm
wrote:

Went to a friends barbeque last night and they had two of these in the
garden, one pointing up at rear house wall (including windows), and
another up to a tree at the end of the garden. Looked amazing.

http://www.outdoordecordirect.com/artifact/2336252/

(American site, but available in UK via Amazon and others).

Are these safe and legal, eg. if you happen to look at one from a few
metres away,

I tend to distrust products which quote irrelevant alphabet soup such
as "Safe: With certificates of FDA, CE, FCC, ROHS and IP65 Test
Report, UL IP44 Power Supply, this laser light is safe and
environment-friendly." Of those "certificates" none are to do with
laser safety. I assume their "5W" should be 5mW but anything is
possible.

Of the two lasers the green is potentially the more harmful as the
green light is produced by a standard laser diode first generating
near infrared light with a wavelength of 808nm. This is focused onto a
neodymium crystal that converts the light into infrared with a
wavelength of 1064nm. In the final step, the light passes into a
frequency doubling crystal that emits green light at a wavelength of
532nm. The beam is reflected back and forward in this process and to
prevent any IR in the beam escaping the laser should incorporate an IR
filter. Many do not.

As IR is invisible the normal blink reflex which gives protection
against direct viewing at low power and visible frequencies doesn't
work. Moreover a green laser with no IR filter may well be below the
5mW limit for visible light but emitting far higher levels of IR.

There is no simple way of testing whether either laser is safe. (it is
possible using a CD as a diffraction grating and a web cam with the IR
filter removed but not easy). Given the number of Chinese lasers
which, when formally tested, fail to meet safety standards (often by a
factor of 10 times or more) the probability is that these are not
safe. There is a strong incentive for manufacturers and online
sellers to produce higher power lasers and label them as 5mW. The
labeling deceives the user into thinking they are safe, the higher
power produces brighter effects and gets them better user reviews.

and what about aircraft if it pointing upwards, given all
the recent problems with handheld lasers around airports?

The problems with lasers and aircraft is not only the potential for
direct eye damage but the potential for distraction during crucial
phases of flight. Any laser, no matter what colour or power, would be
a distraction shining into the cockpit so if you had one regularly
decorating flight paths around you you should expect a visit from the
constabulary sooner or later. (Article 222 of the Air Navigation
Order 2009 " A person must not in the United Kingdom direct or shine
any light at any aircraft in flight so as to dazzle or distract the
pilot of the aircraft. ").

In the advert you quote there are some other things that would point
to the lack of likelihood of the thing ever meeting any safety
standard. For example the use of Chinglish and technobabble :-

"Why your Laser Projector not come with a remote?

Compared to other similar items with remote controls, ours have better
quality and more stable.To use the remote control, you have to aim it
directly at the Infrared sensors or RF sensor, which is not healthy
for naked eye. Based on this, we decided to not include the remote
control for this item."

(Real answer - it would have cost us 50 cents more).