Sitting here listening to my Class A amplification HiFi system & reading your post made me realize you are 100% correct about light heat,watts are watts no matter the intended use & that got me thinking about different types of amplifiers & the different heat created by exact wattage amplifiers of a different Class/design ,the same rules apply with lighting as amplification.
For instance a 600 watt Class A amplifier design generates massive heat due to its design,much like magnetic ballasts,a Class A/B amplifier of the same 600 watts generates less than 1/4 the heat of the Class A design,much like digital ballasts,then there is the Class D design amplifiers most active subwoofers have built in them,they generate nearly zero heat at 600 watts up to 5,000 watt models I've seen,much like LED.
The design of the bulb & ballast, as well as the bulb/ballast efficiency play a huge role in how much radiant heat the bulb creates .
