well yes..however..thats only if they have no shade to escape to..they know how much uvb and heat they need..as long as when they start to get too warm, or have had enough uvb that they can retreat to a shaded place to chill they will be fine...just like people..some sun is good..too much is bad..same with lizards too..thus why they thermoregulate, or hide under rocks, or in the shade of trees.