This web application simulates under water light characteristics such as attenuation(extinction), visibility (Secchi depth) and amount of light remaining at the bottom (bottom light) based on optical active substances measured in the water. The application shows the contribution to the overall extinction coefficient (Kd-PAR) of the various substances that are present in water and affect under water light. Based on this contribution (read the restriction) the effect of measures to improve water quality though improvement of the under water light climate may be evaluated on forehand. Light in water is one of the most important ecological key factors (ESF2).

The light at the water sediment is presented as the remaining percentage of the incoming light at the water surface. The development of macropytes demands a percentage between 2-10% light at the sediment. This web tool uses 4% as a critical lower limit(van den Berg, 2003).

The simulation model of this web tool is based on the model UITZICHT (Buiteveld, 1995) and simulates the light under water on the basis of spectral properties of light and the absorption and reflection of water and all optically active substances available in water.

The module is built by Deltares for STOWA (Foundation for Applied Water Research) which is the knowledge centre for regional water management in the Netherlands. STOWA develops, collects and disseminates knowledge that is needed by regional water managers.

Which input is required?

Beside depth of the water the module requires the four variables below.

Enter characteristic values for a sampling location in the yellow coloured fields. The application can propose the required input from other measurements. Enter if desired the blue coloured fields and then use the button "Suggest input for UITZICHT".

Specific optical properties vary by lake or water type (Bakema, 1988 en Hekkink en Blom, 1994). By default he application makes use of set of parameters Buiteveld reports for lake IJsselmeer in the Netherlands, in addition parameters from one of the lakes reported in Buiteveld (Marker, Wolderwijd and Volkerak) may be used.

Water depth [m] 
Suspended matter concentration (seston) [mg/l] 
Percentage ignition residue in suspended matter [%] 
Chlorophyll concentration [ug/l] 
Dissolved organic carbon (DOC) [mg/l] 
.....use data from example lakes 
Detritus [mg/l] 
ignition residue [mg/l] 
Absorption humics at 380 nm [m-1

User dependant output, e.g. location
User dependant output, e.g. date and time


Sechhi depth :  dm
light at the sediment :  %
KD for 4% bottom light : m-1
Depth 4% light :  m
Depth 10% light (550nm) :  m
██Variable 10.0m-10 %
██Variable 20.0m-10 %
██Variable 30.0m-10 %
██Variable 40.0m-10 %
██Variable 50.0m-10 %

 Critical lower limit
      macropytes (4% light)

 % light (sufficient voor

 % light (insufficient for