Finding the first index in a list greater than a particular value

[Atri Mahapatra]

I have a list of dictionaries which look like this:
[{'Width': 100, 'Length': 20.0, 'Object': 'Object1'}, {'Width': 12.0, 'Length': 40.0, 'Object': 'Object2'}...... so on till 10] 

I would like to find the first index in the list of dictionaries whose length is greater than a particular value

f=lambda seq, m: [ii for ii in range(0, len(seq)) if seq[ii]['Length'] > m][0] and it throws an error

can  anyone suggest a way  to do it?

Thanks,
Atri