You are watching the skin the entire time you are treating.
What you are looking for:
Heat buildup
Client response
Changes in texture or tone
How the skin is handling each pulse
A visible reaction is not required for an effective treatment. Some clients will show clear perifollicular edema and redness. Others will show very little, especially in deeper skin tones.
PFE and mild redness can be indicators of effective treatment, but are not required in every client.
Do not chase a reaction.
You are not treating for redness. You are treating to effectively target the follicle.