Heat gain distributions for LED lighting are given report in ASHRAE RP-1681 "Low Energy LED Lighting Heat Distribution in Buildings", summarized in this paper (paywall), and heat gain for fluorescent luminaires and other types are in ASHRAE RP-1282 "Lighting Heat Gain Distribution in Buildings". If you are an ASHRAE member, you can access these research reports for free online through the ASHRAE technology portal.

Some heat gain fractions for fluorescent and incandescent luminaires are list in the EnergyPlus Input Output Reference.