SSDI vs Widow Benefit

It looks like the benefit available to disabled survivors at age 50 is 70.5 percent, not 75 percent, of the deceased worker's benefit amount.

You can receive widows/widowers benefits based on your age at any time between age 60 and your full retirement age as a survivor. However, if you start at an earlier age, your survivors benefits are reduced a fraction of a percent for each month before your full retirement age.

Here are two useful sources for this :

http://www.ssa.gov/survivorplan/ifyou5.htm
http://www.ssa.gov/survivorchartred.htm