• Question: do the suns tanning rays penetrate water and to what degree

    Asked by jjfarooq to Dalya, Derek, Sarah, Tim, Tom on 19 Jun 2011.
    • Photo: Sarah Thomas

      Sarah Thomas answered on 16 Jun 2011:

      Sun tanning rays are called ultraviolet light (UV) and yes they can penetrate water. Within UV light, there is a spectrum of colour called the electromagnetic spectrum. The different colours within UV light can penetrate different depths, but generally the colours at the higher end of the spectrum, penetrate deepest. The blue wavelength of UV light can penetrate down to depths of 200 feet. This is said to by why deep water appears bluish.

    • Photo: Derek McKay-Bukowski

      Derek McKay-Bukowski answered on 16 Jun 2011:

      Sun tanning is caused by ultraviolet (UV) light. This is split into two broad ranges (called UVA and UVB), which have slightly different effects. The wavelengths of these (in nm = nanometres) are:

      UVA = 320 to 400 nm (which includes part of the violet and blue visible light)
      UVB = 250 to 320 nm

      The absorption (in units of 1-per-cm) are:

      250nm = 0.0019
      300nm = 0.0004
      320nm = 0.0002
      350nm = 0.00012
      400nm = 6.00E-05

      Reference: K. S. Shifrin, “Physical Optics of Ocean Water” (1988).
      Source: http://omlc.ogi.edu/spectra/water/abs/index.html

      As you can see these are small numbers. That means that UV can certainly penetrate water (especially UVA). Blue light (around 380 – 400 nm) very easily goes through water, as Sarah says. However the colour of deep water can also be affected by other things, such as marine life, dissolved chemicals and other factors.

    • Photo: Tom Crick

      Tom Crick answered on 18 Jun 2011:

      Further to the other answers: yes, you have to be very careful when you are in water, as you can still easily get sunburnt — that’s why most suncreams are water resistant!

    • Photo: Tim Millar

      Tim Millar answered on 19 Jun 2011:

      As above