The Recommended Practices (RPs) available from NCSLI (National Conference of Standards Laboratories - International) provide some guidance on lab environmants. http://www.ncsli.org
Generally the guidelines for dimensional: 20 C +/- 2 C, 30% to 40% RH.
Electrical/electronic: 23 C +/- 3 C, 40% to 50% RH.
Hope this helps.