davidgdg
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With the increasing popularity of Blu Ray units, I had a hunt on the Web to see if they pose any particular risks beyond those posed by green and red.
The main eye risk posed by green, red and IR lasers is thermal - i.e. heating of the retina. The dangers are well understood and fairly easy to quantify.
However, it seems that blue (and more relevantly Blu Ray - 405nm) might (I stress "might" - the jury is out) pose an additional risk of retinal damage at levels that would be too low to cause thermal damage. This is different from the well-known risk of cataracts posed by true UV light.
I have been reading some articles online about this. There is some evidence that wavelenths of 400-480 nm (with peaks at 400 and 450) can cause photochemical damage which may contribute towards macular degeneration. The problem is known as "blue light hazard". The danger is not limited to coherent (i.e. laser) light but applies to ordinary blue light sources too. However, Blu Ray in particular appears quite dim and so may pose an additional hazard.
Note that there seems to be no consensus on this. Some articles say there is no additiona risk. Others say there is.
There is a long piece on the subject generally (but without reference to lasers) at
http://www.sunnexbiotech.com/therapist/blue light damage.html
As far as laser exposure is concerned, this says there is no additional risk posed by blue laser light versus green or red:
http://www.ehs.uci.edu/programs/radiation/UCI LASER SAFETY NEWSLETTER VI, 1.pdf
But on the other hand, this suggests there is:
http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1298235&blobtype=pdf
The pubmed piece above refers in particular to research done in the 1960s that suggests that exposure to light levels on the retina of 0.27 watts/cm2 can cause retinal damage within about 15-20 minutes of exposure. Although the article does not say so, it was presumably the blue element that would have done the damage (photochemical) because the heat (thermal) level would have been too low to cause damage.
A back-of-an-envelope calculation sugggests that 0.27 watts/cm2 equates to viewing the spot made by a 150mw blu ray at a distance of about 7 feet on a diffusely (i.e. non-mirror) reflecting surface.
I am not an expert on any of the above, but it looks as though to be safe for a high power Blu Ray, indoor spot viewing at distances of less than 7 feet should be regarded as potentially hazardous (especially in darkness). For burning, use of goggles with Blu Ray should therefore be regarded as essential (and more important than with equivalent green or red powers, where the risk is more one of temporary glare than long term damage). Outdoor use is probably safe without goggles except on reflective surfaces at close range.
The main eye risk posed by green, red and IR lasers is thermal - i.e. heating of the retina. The dangers are well understood and fairly easy to quantify.
However, it seems that blue (and more relevantly Blu Ray - 405nm) might (I stress "might" - the jury is out) pose an additional risk of retinal damage at levels that would be too low to cause thermal damage. This is different from the well-known risk of cataracts posed by true UV light.
I have been reading some articles online about this. There is some evidence that wavelenths of 400-480 nm (with peaks at 400 and 450) can cause photochemical damage which may contribute towards macular degeneration. The problem is known as "blue light hazard". The danger is not limited to coherent (i.e. laser) light but applies to ordinary blue light sources too. However, Blu Ray in particular appears quite dim and so may pose an additional hazard.
Note that there seems to be no consensus on this. Some articles say there is no additiona risk. Others say there is.
There is a long piece on the subject generally (but without reference to lasers) at
http://www.sunnexbiotech.com/therapist/blue light damage.html
As far as laser exposure is concerned, this says there is no additional risk posed by blue laser light versus green or red:
http://www.ehs.uci.edu/programs/radiation/UCI LASER SAFETY NEWSLETTER VI, 1.pdf
But on the other hand, this suggests there is:
http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1298235&blobtype=pdf
The pubmed piece above refers in particular to research done in the 1960s that suggests that exposure to light levels on the retina of 0.27 watts/cm2 can cause retinal damage within about 15-20 minutes of exposure. Although the article does not say so, it was presumably the blue element that would have done the damage (photochemical) because the heat (thermal) level would have been too low to cause damage.
A back-of-an-envelope calculation sugggests that 0.27 watts/cm2 equates to viewing the spot made by a 150mw blu ray at a distance of about 7 feet on a diffusely (i.e. non-mirror) reflecting surface.
I am not an expert on any of the above, but it looks as though to be safe for a high power Blu Ray, indoor spot viewing at distances of less than 7 feet should be regarded as potentially hazardous (especially in darkness). For burning, use of goggles with Blu Ray should therefore be regarded as essential (and more important than with equivalent green or red powers, where the risk is more one of temporary glare than long term damage). Outdoor use is probably safe without goggles except on reflective surfaces at close range.
