There are many factors that need to be considered when it comes to the correct amount of photons (light) that is required for optimal growth. Usually people just look at the size of area that needs to be covered. More importantly what is the size of the canopy you are covering? Other factors that determine the appropriate amount light are: What strain or strains are you growing? What source of light are you using? (In your case 600 watt HPS. Are these single or double-ended?) Are you able to maintain proper VPD's? Are you supplementing CO2? In general cannabis is a light hungry plant. The most precise way to determine your light levels you will need to use a light meter that reads PAR. Flowering cannabis can require anywhere from 500 micromoles to 1000+. 

Light spectrum might be one of the most underrated factors when it comes to cannabis production. Not only only does light affect the plant health but also the environment in which the plant is growing in. Having better control of your environment allows for more consistent production and overall health of the plant. When it comes to specific spectrums for cannabis there is a lot of information that points to the benefits of having a full spectrum.

Heliospectra has also done extensive studies on this and that is why our LED is not only full-spectrum but blended light as well. Having green light within your spectrum allows for denser canopies due to the green's abilty to penetrate through the leaves. 

We are also finding that cannabis is very responsive to the wavelength of light in the far red region as well. This is a very specific wavelength that trigges the flowering response in flowering plants. This will accelerate flowering and decrease your flowering times 5-14 days(strain dependent). 

You can also start to control secondary metabolite production with spectrum manipulation. Many growers will expose their plants just to blue light just days before harvest to increase THC and terpenes. 

Lastly having the correct spectrum of light keeps an overall healthier plant. Their natural resistance to pest and molds becomes greater. With IPM becoming more and more important everyday this will assist in these efforts rather than working against you. 

To simply answer our lights produce half the heat of a standard air-cooled 1000-watt HPS and two-thirds less heat than a 1000-watt DE HPS. The BTUs produced by our LX60 light at max output is up to 2150 BTUs. One factor to also consider while LEDs do run cooler, your grow-room environment should run between 80-85 degrees fahrenheit. This will also ease the workload on your HVAC.

To better answer your question I will need a little more detail. What I think you might be asking is if its better to grow under LED and then trasition to an HID? This is very typical of growers who just want to get their feet wet in the LED market while lowering their overall energy consumption. Going to an HID light for flowering is not necessary anymore with the qualtiy of LED grow lights that are in the market today. Yop will also notice stress occurs when switching from LED to HID. This can be very minimal if the HID lights are turn down to the lowest setting and very far away from the plant canopy for a couple days.