I tried to germinate lettuce indoors at 27 degrees Celcius (80 degrees Fahrenheit) in the day and 17 degrees Celsius (62 degrees Fahrenheit) at night, but they did not germinate. What is the most favourable day and night temperature for Grand Rapids lettuce seeds germination?.
It does sound quite hot for lettuce germination. For those of us in the US, that works out to 62F at night, 81F during the day. Grand Rapids is an heirloom variety from here where I live in the Great Lakes region, where lettuce is grown in the spring and fall. That means temperatures generally hover in the 40's at night (around 4-8C) and only get into the 60's during the day (17C). Given that the climate you are trying to grow in is very different, you might do better with a different variety.