How to use > or < in LOOKUP formula?

[CC]

I am trying to search a row of numbers for the first occurence of a number

=500 and return the date at which the number is found, where the dates are

the column headings in the spreadsheet. I can use LOOKUP to find the date
where the value = 500 but I need to find when it becomes >=500.

 

[JMB]

if the values are in row 2 and dates in row 1, try:

=LOOKUP(1,1/(2:2>=500),1:1)